Lead acid battery management system

Abstract

A Lead-Acid Battery Management System (BMS) and a method for operating a BMS for a battery system comprising a plurality of groups of at least one lead acid battery, the battery management system comprising: at least one control device configured to electrically integrate and segregate each of the batteries from the string, and a controller configured to control the control device to independently control the charging and discharging of each of the batteries. In some cases the controller is configured to determine an input power available to charge the battery system, determine, based on the determined input power, that at least one of the groups of batteries can charge above a charging threshold; and selectively charge at least one of the groups of at least one battery. In some cases the BMS is configured overcharge the batteries independently. In some cases the BMS is configured to modify the discharging of the at least one battery based in a determined charge characteristic.

Description

Lead Acid Battery Management SystemTECHNICAL FIELD

[0001] The present disclosure generally relates to battery management systems for lead acid batteries and methods for controlling the battery management system.BACKGROUND

[0002] Battery storage is becoming an increasingly popular addition to home energy management (HEM) systems and / or energy storage systems (ESS). Lead acid batteries (LABs), typically comprise a plurality of inaccessible cells within each battery and provide a low-cost solution for energy storage. However, historically LABs have suffered from poor lifetimes and low depth of discharge (often only 40% to 60% of the charge in the battery can be discharged) and or battery failure when compared to technologies such as lithium-ion.

[0003] Lead acid batteries are commonly arranged in groups (also referred to as strings) or modules. Groups allow a plurality of batteries to be combined to increase the overall stored energy and / or to provide a greater output voltage and / or greater output current. Groups can be arranged with batteries in series, parallel or parallel and series. Typically lead acid batteries are arranged in series configurations, up to around 1000 VDC, and then a second (and more) parallel groups(s) will be added where additional capacity is required. The parallel groups allow charging and discharging of the batteries as a combined action. In this manner, each battery within battery system will ideally discharge the same amount, and charge the same amount, so that each battery in the system will be at the same state of charge at all times.

[0004] In practice there is a high variance between similar lead acid batteries. For example, in a series string, individual batteries within the string will be exposed to different charging / discharging voltages. The batteries that see the highest charging voltages will have higher gassing rates and be exposed to higher degrees of water loss and grid corrosion than batteries with the lowest charging voltages changing their electrical performance. In a parallel string, differing battery voltages and / or impedances will result in different charge and discharge currents and therefore states of change between batteries within the string. The LABs that see the highest charge and discharge currents will swing though larger state of charge windows and will therefore work harder and wear out faster than other members of the string.

[0005] Different types of LABs may be used. For example, prismatic batteries, absorbent glass mat (AGM) and bipolar batteries. Prismatic or monopolar batteries have separate positive and negative electrodes, with electrical connections required between adjacent cells. Bipolar batteries have a plurality of cells arranged in series, with adjacent cells sharing electrodes, so that one cells negative electrode, and another cells positive electrode are located next to each other.

[0006] US9711976B2 shows a prior art system using a lead acid storage battery bank. The lead acid batteries are arranged in series strings and a state-of-charge (SoC) model is used to determine when to apply an equalization charge to equalize the SoC of all batteries in the series string. US971 1976B2 suggests how to estimate the SoC of each battery and reduce the number of equalization charges required.

[0007] Maintaining the health of LABs requires careful management of the charging and discharging, as well as consideration of the state of the electrolyte between the LABs. The management of LABs differs from other battery types, where different chemistries are used (such as lithium ion). Moreover, in many cases there are competing requirements, so that a battery management system (BMS) must be carefully designed to improve overall performance. Due to the different chemistries of the batteries, operating parameters required for the batteries and different battery arrangements, one size fits all battery management system cannot be applied or used across these different battery types. Currently, lithium Ion, or hybrid battery packs have been preferred for energy storage due to the longer lifetimes and / or deeper cycling possible with these technologies.

[0008] It is an aim of the disclosure to provide a BMS for LABs and / or a method of operating a BMS for LABs that extends the effective lifetime of the LABs or at least that substantially mitigates the above product limitations.SUMMARY

[0009] Aspects of the disclosure address one or more of the above problems by providing a lead acid battery management system and / or a method of managing a plurality of lead acid batteries that increases the lifetime of the lead acid batteries in the battery system or address one or more of the problems associated with prior art systems or at least provides a choice.

[0010] Aspects of the disclosure address one or more of the above problems by providing a lead acid battery management system for charging a battery system comprising a plurality ofgroups of at least one lead acid battery each, the battery management system comprising: at least one control device configured to electrically integrate and segregate each of the groups of at least one battery from the battery system, and a controller configured to control the control device to independently control the charging and discharging of each of the groups of at least one battery wherein the controller is configured to: determine an input power available to charge the battery system, determine, based on the determined input power, that at least one of the groups of batteries can charge above a charging threshold; and selectively charge at least one of the groups of at least one battery.

[0011] In some cases, comprising the steps of: determining a number of the groups of at least one battery to be charged dependent on the determined input power; and selectively charging the determined number of groups of at least one battery. In some cases, the charging threshold is a cell charging potential threshold. In some cases, the charging threshold is a desired positive half-cell overpotential. In some cases, the charging threshold is determined based on a desired positive half-cell overpotential. In some cases, the desired positive half-cell overpotential threshold is any one or more of: at least 100mV, at least 150mV or at least 200mV. In some cases, the charging threshold is a threshold of an electrical characteristic of the lead acid batteries dependent on the positive half-cell overpotential. In some cases, the selective charging of the at least one groups of at least one battery is controlled to achieve the desired positive half-cell overpotential.

[0012] In some cases, the controller is configured operate in real-time. In some cases, the charging threshold is a threshold of an electrical characteristic from which the positive half-cell overpotential can be inferred. In some cases, the electrical characteristic is a charging potential, optionally wherein the positive half-cell overpotential is inferred based on the charging potential and the open circuit potential. In some cases, a charging current threshold is determined, the charging current threshold configured to generate the positive half-cell overpotential above the threshold. In some cases, the positive half-cell overpotential is above 200mV

[0013] In some cases, the controller is configured to: control a charge rate to maintain charging above the charging threshold. In some cases, the charging threshold is a minimum charging current. In some cases, the minimum charging current is based on the capacity of each of the plurality of groups of at least one battery. In some cases, the minimum charging current is predetermined. In some cases, the minimum charging current threshold comprises acharge rate, optionally wherein the charge rate is based on 5C capacity of the plurality of groups of at least one battery. In some cases, the minimum charging current threshold is between 0.7 and 1.4C, optionally at least 1C.

[0014] In some cases, the charging threshold is applied below a threshold state of charge of each group of at least one battery. In some cases, the threshold state of charge is any one of 40%, 45%, 50%, 55% or 60%. In some cases, comprising a charger, wherein determining the input power availability comprises determining a rated power of the charger. In some cases, determining the available input power comprises: receiving one or more measurements; and determining the available input power from the one or more measurements. In some cases, the groups of at least one battery are connected to the battery system in parallel. In some cases, the controller is configured to monitor the state of charge of each of the groups of at least one battery, optionally with a coulomb counter.

[0015] In some cases, the batteries comprise bipolar lead acid batteries. In some cases, the controller is configured to substantially balance the state of charge of each of the batteries in the battery string by rotating which of the groups of at least one battery are being charged. In some cases, the rotation is based on one or more of: a state of charge added to the group of at least one battery, a temperature of the group of at least one battery, and / or a time of charging of the group of at least one battery. In some cases, the controller is configured to determine a temperature of at least one group of the groups of at least one battery and adjust the charging threshold dependent on that temperature.

[0016] In some cases, the temperature comprises one or more of: an internal battery temperature, an external battery temperature, or temperature from which the internal battery temperature can be inferred. In some cases, the controller is configured to determine an ambient temperature surrounding the at least one group, and adjust the charging threshold dependent on that temperature. In some cases, the controller is configured to rotate which of the groups of at least one battery are being charged, optionally wherein the controller is configured to modify the time between charging of each of the groups of at least one battery based, or the number of groups of at least one battery being charged, based on a temperature of the groups or of at least one battery. In some cases, the battery management system is configured to receive power from a solar power source and / or a wind power source.

[0017] In some cases, the controller is configured to: Selectively charge each of the groups of at least one battery to one of: a first target battery state of charge, and an overcharge above afull state of charge, the overcharge greater than the first target battery state of charge, wherein the selection of the first target state of charge or overcharge is dependent on a charge characteristic of each battery.

[0018] In some cases, the charge characteristic comprises any one or more of: a number of charges of each of the batteries to the first target battery state of charge, and / or a length of time since the last charge of each of the batteries to the over charge , and / or a state of charge of each of the batteries during discharge, and / or an electrical characteristic of each of the batteries.

[0019] In some cases, the controller is configured to: receive a measurement of an electrical characteristic of each of the groups of at least one battery, determine a charge characteristic of at least one group of at least one battery from the electrical characteristic; and modify the discharging of the group of at least one battery based in the determined charge characteristic. In some cases, the charge characteristic comprises a state of charge. In some cases, the discharge is modified by any one or more of: preventing discharge of the at least one battery; decreasing a discharge rate; an over-discharge characteristic.

[0020] In some cases, the charging threshold is applied for a first portion of a charge. In some cases, the first portion comprises a first percentage of capacity returned to the battery, optionally wherein the first percentage comprises 0.5%, 1 % or 2% of state of charge.

[0021] In some cases, each of the plurality of groups of at least one battery have the same capacity. In some cases, the rate minimum charging current threshold is at least 0.5C. Optionally substantially 1 C. Optionally between 0.7 and 1 ,5C. Optionally between 0.8 and 1 ,2C. In some cases, the minimum charging current threshold is predetermined based on an expected current required to achieve a desired positive half-cell overpotential. In some cases, the threshold current is applied across a state of charge range of each group of at least one battery. Optionally the range comprises between 20 and 60 SoC, between 20-50 SoC, between 30 and 50 SoC, or between 30 and 60 SoC. In some cases, the charging threshold is dependent on a state of charge of each group of at least one battery. In some cases the measurements measure a current or voltage received by the battery system. In some cases comprising a coulomb counter associated with each of the groups of at least one battery In some cases the charger is configured to supply at least 1 C to each of the plurality of groups of batteries, optionally but not the whole battery system.

[0022] In some cases each of the groups of batteries comprises a plurality of the batteries in series. In some cases each of the groups of batteries are connected in either one of series or parallel. In some cases each of the groups of the batteries consist of a single battery. In some cases each lead acid battery comprises a single cell battery, or a multicell battery.

[0023] Aspects of the disclosure address one or more of the above problems by providing a method of managing a plurality of lead acid batteries in a battery system, the battery system comprising a plurality of groups of at least one lead acid battery each, the method comprising the steps of: determining an input power available to charge the battery system, determining, based on the determined input power, that at least one of the groups of batteries can charge above a charging threshold; and selectively charging at least one of the groups of at least one battery. In some cases one or more of the features or steps of the system above are incorporated.

[0024] Aspects of the disclosure address one or more of the above problems by providing a method of managing a plurality of lead acid batteries in a battery system, the battery system comprising a plurality of groups of at least one lead acid battery each, the method comprising the steps of: determining a charge current required to achieve a desired positive half-cell potential; selectively charging each at least one of the groups of at least one battery at or above the determined charge current.

[0025] In some cases comprising the step of rotating the selective charging between each of the groups of at least one battery to substantially maintain balanced state of charge in each of the groups. In some cases comprising the steps of monitoring a cell charging potential and determining if the desired positive half-cell potential is achieved. In some cases comprising the step of controlling the charge current to achieve the desired positive half-cell potential. In some cases comprising the step of maintaining the desired positive half-cell at the start of charge when the said at least one lead acid battery or groups of at least one lead acid battery is at a low state of charge.

[0026] Aspects of the disclosure address one or more of the above problems by providing a method of managing a plurality of lead acid batteries in battery system, the battery system comprising a plurality of groups of at least one lead acid battery each, the method comprising the step of: Independently charging each of the groups of at least one battery at or above a 1 C charge rate for at least an initial portion of a charge cycle.

[0027] In some cases the initial portion comprises the first 1 , 2, 5, 10, 15, 20, 30, 40 or 50% of the charge cycle. In some cases the initial portion r is for a pre-determined time period based on any one of the at least one lead acid battery characteristics. . In some cases comprising the step of rotating charging between each of the groups of at least one battery.

[0028] Aspects of the disclosure address one or more of the above problems by providing a lead acid battery management system for charging a battery system comprising a plurality of groups of at least one lead acid battery each, the battery management system comprising: at least one control device configured to electrically integrate and segregate each of the groups of at least one battery from the battery system, and a controller configured to control the control device to independently control the charging and discharging of each of the groups of at least one battery

[0029] wherein the controller is configured to: determine battery temperature of at least one of the groups of batteries and / or the battery system, Determine, based on the temperature, a maximum charging threshold and / or a minimum time between charges, and to selectively charge at least one of the groups of at least one battery based on the maximum charging threshold and / or a minimum time between charges. In some cases the maximum charging threshold limits a charge rate of the charging. In some cases the minimum time between charges determines a number of the groups of at least one battery to charge concurrently and / or a rest period between charges of any of the groups of at least one battery.

[0030] In an aspect the disclosure may broadly be said to consist in a lead acid battery management system for charging a battery system comprising at least one battery string comprising a plurality of lead acid batteries, or a plurality of groups of at least one lead acid battery, the battery management system comprising: at least one control device configured to electrically integrate and segregate each of the strings or groups of batteries from the battery system,, and a controller configured to control the control device to independently control the charging and discharging of each of strings or groups of batteries.

[0031] In some cases the groups of batteries are connected in parallel. In some cases comprising one or more sensors associated with each of the groups of batteries. In some cases the sensors are configured to sense at least one of: the electrical characteristics of at least one of the groups of batteries and the power flow to and from at least one of the groups of batteries. In some cases the sensors comprise any one or more of current sensors and / or voltage sensors. In some cases the sensors comprise a current counter or a coulomb counter.

[0032] In some cases the batteries comprise prismatic lead acid batteries including for example flooded lead acid batteries, tubular lead acid batteries, and the like. In some cases the batteries comprise valve regulated lead acid (VRLA) batteries, including for example Absorptive Glass Mat (AGM) lead acid batteries and / or gel batteries. In some cases the batteries comprise bipolar lead acid batteries. In some cases the batteries comprise an electrode framework that comprises a network suitable to provide structural form to a paste and / or to retain the same within the framework. In some cases the electrode framework comprises fabric structured electrodes. In some cases the fabric structured electrode(s) comprises a fibrous material, such as a carbon fibre and / or a glass fibre. In some cases the fibrous material is a non-conductive fibrous material such as for example an oxidised polyacrylonitrile (PAN) fibre (OPF), glass fibre, silicon carbide fibre or alumina fibre. The fibre material may be a woven material (comprising intersection warp and weft fibres), a knitted material, or a non-woven material such as a fluidentangled, for example hydro entangled, material and / or a felt material or knitted fibre material.

[0033] In some cases the one or more control devices comprise one or more switches. In some cases the switches comprise MOSFETs. In some cases comprising a charger. In some cases comprising a charger configured to electrically connect the battery system to an AC power network. In some cases the controller is configured to control the charger, such as an inverter. In some cases the controller is configured to substantially balance the state of charge of each of the groups of batteries in the battery system. In some cases the battery management system is configured to receive power from an intermittent energy source.

[0034] In some cases the intermittent energy source comprises any one or more of a solar power source and / or a wind power source. In some cases the solar power source comprises one or more solar panels and / or the wind power source comprises one or more wind turbines. In some cases the battery management system is configured to connect to a power grid, to receive and / or transmit power to the power grid. In some cases the battery management system is configured to monitor the state of charge of each of the plurality of batteries during operation of the battery system. In some cases the battery management system is configured to substantially balance the state of charge of each of the plurality of groups of batteries within 25% SoC, 20% SoC, 15% SoC, 10% SoC, 5.0% SoC, 4% SoC, 3% SoC, 2.5% SoC, 2% SoC, or 1 %SoC. In some cases the battery management system is configured to substantially balancethe state of charge of each of the plurality of groups batteries within 1 .5% SoC, 1 % SoC, 0.5% SoC, 0.25% SoC or 0.15% SoC.

[0035] In some cases the controller is configured to: selectively charge each of the plurality of groups batteries to one of: a first target battery state of charge, and an overcharge above a full state of charge; the overcharge greater than the first target battery state of charge, wherein the selection of the first target state of charge or overcharge is dependent on a charge characteristic of each battery.

[0036] In some cases the charge characteristic comprises any one or more of: a number of charges of each of the groups of batteries to the first target battery state of charge, and / or a length of time since the last charge of each of the batteries to the over charge , and / or a state of charge of each of the groups of batteries during discharge, and / or an electrical characteristic of each of the batteries. In some cases the controller is configured to charge each of the plurality of groups of batteries to the first target state of charge substantially concurrently. In some cases concurrent charging comprises rotating the groups of batteries being charged.

[0037] In some cases each of the plurality of groups batteries are charged to the overcharge independently. In some cases the first target battery state of charge comprises a substantially full state of charge of each battery. In some cases the full state of charge comprises 95-105% battery capacity. In some cases the overcharge comprises an overcharge of 5% to 20% battery state of charge. In some cases the overcharge comprises any one or more of 5%-40% overcharge or 20% to 40% overcharge.

[0038] In some cases the controller is configured to determine an input power available to charge the battery system. In some cases determining the input power comprises receiving a measurement of an input power available to charge the battery system. In some cases the controller is configured to determine a number of the plurality of groups of batteries to be charged dependent on the available input power, a charging threshold; and to selectively charge the determined number of batteries.

[0039] In some cases the charging threshold comprises a minimum charging current threshold. In some cases the charging current threshold comprises a charging current density threshold of each or all of the groups of batteries. In some cases the charging threshold is configured to provide a sufficient input power to one or more of the groups of batteries. In some cases each group of batteries has the same charging threshold. In some cases each group of batteries comprises a different charging threshold. In some cases the group of batteries to be selectivelycharged are determined based on their charging thresholds. In some cases the charging threshold is dependent on a state of charge of each group of battery. In some cases the charging threshold is dependent on the state of charge of the group of batteries. In some cases the battery management system is configured to rotate which of the plurality of groups batteries are selectively charged. In some cases the rotation of the plurality of groups of batteries is determined based on the state of charge of each of the groups of batteries. In some cases the rotation of the plurality of groups of batteries is determined based on a charge characteristic of each of the batteries.

[0040] In some cases the controller is configured to: receive a measurement of an electrical characteristic of each of the plurality of groups batteries, determine a charge characteristic of at least one battery of the plurality of groups of batteries from the electrical characteristic; and modify the discharging of the at least one group of batteries based in the determined charge characteristic.

[0041] In some cases the charge characteristic comprises a state of charge. In some cases the discharge is modified by preventing discharge of the at least one group of at least one battery. In some cases the discharge is prevented for a predetermined period of time. In some cases the charge characteristic comprises a battery capacity. In some cases the discharge is modified to decrease the discharge rate. In some cases the group of batteries is discharged to a state of charge below 20%. In some cases the charge characteristic comprises an over-discharge characteristic. In some cases further discharge is prevented until after a charge cycle. In some cases the charge cycle comprises a charge to 100% state of charge or an overcharge of at least 2%, 5%, 10%, 15% or 20%. In some cases the received measurement comprises any one or more of: a coulomb count, a current, a voltage.

[0042] In a further aspect the disclosure may broadly be said to consist in a method of managing a plurality of groups of at least one lead acid batteries in a battery system, the method comprising: selectively charging each of the plurality of groups of batteries to one of: a first target battery state of charge, and an overcharge above a full state of charge, the overcharge greater than the first target battery state of charge, wherein the selection of the first target state of charge or overcharge is dependent on a charge characteristic of each group of batteries or at least one battery in said group of batteries.

[0043] In some cases the charge characteristic comprises any one or more of: a number of charges of each of the groups of batteries to the first target battery state of charge, and / orlength of time since the last charge of each of the groups of batteries to the overcharge , and / or a state of charge of each of the groups of batteries during discharge, and / or an electrical characteristic of each of the groups of batteries. In some cases comprising charging each of the plurality of groups of batteries to the first target state of charge substantially concurrently. In some cases comprising charging each of the plurality of groups of batteries to the overcharge independently. In some cases the first target battery state of charge comprises a substantially full state of charge of each group of at least one battery. In some cases the full state of charge comprises 95-105% battery capacity. In some cases the overcharge comprises an overcharge of between 2% to 20%. In some cases the overcharge comprises an overcharge within the range of between 102-105%, 105-1 10%, 110-1 15%, 115-120%, 120-125%, 125-2- 140% battery overcharge or from 20% to 40% battery overcharge.

[0044] In a further aspect the invention may broadly be said to consist in a method of managing a plurality of groups of at least one lead acid battery(s) in a battery system, the method comprising: determining an input power available to charge the battery system, determining a number of the plurality of groups of batteries to be charged dependent on the input power measurement and a charging threshold; and selectively charging the determined number of groups of batteries. In some cases determining an available input power comprises receiving one or more measurements of an input power available.

[0045] In some cases the charging threshold comprises a minimum charging current threshold. In some cases the charging threshold comprises a charging current density threshold of each or all of the groups of batteries. In some cases the charging threshold is configured to provide a sufficient input power to one or more of the groups of batteries. In some cases each group of batteries has the same charging threshold. In some cases each group of batteries comprises a different charging threshold. In some cases comprising selecting the groups of batteries to be charged based on their charging thresholds. In some cases the charging threshold is dependent on a state of charge of each group of batteries. In some cases the charging threshold is dependent on the state of charge of all or each of the groups of batteries. In some cases comprising rotating which of the plurality of groups of batteries are selectively charged. In some cases the rotation of the plurality of groups of batteries is determined based on the state of charge of each of the batteries. In some cases wherein the rotation of the plurality of groups of batteries is determined based on a charge characteristic of each of the groups of batteries.

[0046] In a further aspect the disclosure may broadly be said to consist in a method of managing a method of managing a plurality of groups of at least one lead acid battery in a battery system, the method comprising: determining a measurement of an electrical characteristic of each of the plurality of groups of batteries, determining a charge characteristic of at least one group of batteries in the battery system from the electrical characteristic; and modifying the discharging of the at least one battery based on the determined charge characteristic. In some cases determining comprises receiving and / or measuring.

[0047] In some cases the charge characteristic comprises a state of charge. In some cases the discharge is modified by preventing discharge of the at least one group of batteries. In some cases the discharge is prevented for a predetermined period of time. In some cases the charge characteristic comprises a capacity of one or more of the groups of batteries. In some cases the discharge is modified to decrease the discharge rate. In some cases discharging the group of batteries comprises to a state of charge below 20%. In some cases the charge characteristic comprises an over-discharge characteristic. In some cases further discharge is prevented until after a charge cycle. In some cases the charge cycle comprises an overcharge to at least 100%, 101 %, 102%, 105%, 110%, 115% or 120% of state of charge. In some cases the received measurement comprises any one or more of: a coulomb count, a current, a voltage.

[0048] In a further aspect the disclosure may broadly be said to consist in a method of managing a method of managing a plurality of groups of at least one lead acid battery in a battery system comprising any one or more of the methods of the other aspects. In some cases the battery system is a parallel string. In some cases the battery system is configured to manage a hierarchy of groups of batteries. In some cases the hierarchy comprises a first level comprising first groups of batteries, and a second level which controls sub-groups of batteries in each of the first groups. The described methods and systems can be applied to one or more levels of the hierarchy. In some cases a third level controls sub-groups of the second level groups of batteries. In some cases further levels are used.

[0049] In a further aspect the disclosure can in any one more examples or configurations of the method described of the disclosure carry out said methods in real time. In some cases taking into account any one or more of: variable power input(s), groups of one or more batteries during charging and / or discharging; State of Health of the groups of at least one battery; temperature of the groups of at least one battery and / or any other battery characteristic. In some cases the real time control is configured to ensure the battery system isoptimised. In some cases the controller may receive external data to optimise battery performance. In some cases the external data may relate to one or more of: an external control signal, variable power input, ;climatic conditions; power use history (for example the users previous monthly, yearly or daily power usage, although this power use history is not limited to the current user), predicted energy demand in the coming minutes, hours or days, predicted energy supply constraints, conditions or price signals from the power grid, and such other external data to enable the battery system to be optimised.

[0050] Features from one or more embodiments or configurations may be combined with features of one or more other embodiments or configurations. Additionally, more than one embodiment or configuration may be used together in a battery management system during a process of charging and / or discharging batteries. Headings and subheadings, if any, are used for convenience only and do not limit the disclosure.

[0051] As used herein the term "(s)" following a noun means the plural and / or singular form of that noun.

[0052] As used herein the term "and / or" means "and" or "or", or where the context allows both.

[0053] The term "comprising" as used in this specification means "consisting at least in part of". When interpreting each statement in this specification that includes the term "comprising", features other than that or those prefaced by the term may also be present. Related terms such as "comprise" and "comprises" are to be interpreted in the same manner.

[0054] It is intended that reference to a range of numbers disclosed herein (for example, 1 to 10) also incorporates reference to all rational numbers within that range (for example, 1 , 1 .1 , 2, 3, 3.9, 4, 5, 6, 6.5, 7, 8, 9 and 10) and also any range of rational numbers within that range (for example, 2 to 8, 1 .5 to 5.5 and 3.1 to 4.7) and, therefore, all sub-ranges of all ranges expressly disclosed herein are hereby expressly disclosed. These are only examples of what is specifically intended and all possible combinations of numerical values between the lowest value and the highest value enumerated are to be considered to be expressly stated in this application in a similar manner.

[0055] This disclosure may also be said broadly to consist in the parts, elements and features referred to or indicated in the specification of the application, individually or collectively, and any or all combinations of any two or more said parts, elements or features.

[0056] Where specific integers are mentioned herein which have known equivalents in the art to which this disclosure relates, such known equivalents are deemed to be incorporated herein as if individually set forth.

[0057] The disclosure consists in the foregoing and also envisages constructions of which the following gives examples only.BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Specific embodiments and modifications thereof will become apparent to those skilled in the art from the detailed description herein having reference to the figures that follow, of which:

[0059] Figure 1 shows a battery system with two parallel strings, each parallel string consisting of two batteries in series.

[0060] Figure 2 shows a neck formation within the active material of a lead acid battery positive electrode.

[0061] Figure 3 shows the failure of battery current collectors due to oxidation.

[0062] Figure 4 shows a system for determining charge and discharge of a battery system.

[0063] Figure 5 shows example relationships between positive electrode half-cell potentials, with respect to a Ag / AgSCU reference electrode, and charge rates.

[0064] Figure 6 shows a flow chart of the battery management system for constant current charging.

[0065] Figure 7 shows a flow chart of the battery management system for constant voltage charging.

[0066] Figure 8 shows a flow chart of the battery management system for discharge.

[0067] Figure 9 shows a schematic of a battery management system.

[0068] Figure 10 shows a layout of a battery management system with 8 batteries.

[0069] Figure 11 shows a flow chart of the battery management system.

[0070] Figure 12 shows an example operation of a battery management system across morning and midday.

[0071] Figure 13 shows an example operation of a battery management system across afternoon, evening and overnight.

[0072] Figure 14 shows an example method to control the positive overpotential of a lead acid battery, it may be used to keep the positive overpotential above a threshold.

[0073] Figure 15 shows an example cell voltage for the battery of Figure 5, the positive halfcell potential of figure 5 can be inferred from the cell voltage.

[0074] Figure 16 shows current and voltage changes for charging eight batteries in rotation, each battery charged singularly.

[0075] Figure 17 shows temperature changes for charging eight batteries as in Figure 16

[0076] Figure 18 shows current and voltage changes for charging eight batteries in rotation, with batteries charged in pairs.

[0077] Figure 19 shows temperature changes for charging eight batteries as in Figure 18.

[0078] Figure 20 shows current and voltage changes for charging eight batteries in rotation, with batteries charged in fours.

[0079] Figure 21 shows temperature changes for charging eight batteries as in Figure 18.

[0080] Figure 22 shows current and voltage changes for charging eight batteries in rotation, with all batteries charged in concurrently.

[0081] Figure 23 shows temperature changes for charging eight batteries as in Figure 18.DETAILED DESCRIPTIONBattery System and Segregation of Batteries

[0082] A battery system (alternatively referred to as a battery pack) is an arrangement of one or more lead acid batteries (LABs). The LABs are typically arranged in one or more groups or strings. A group of batteries comprises one or more batteries. By using series and / or parallel groups the battery system can be built to a target voltage and / or capacity. For example, a battery system may be labelled a 4S2P. This means that the battery system has two parallel strings, and each of the parallel strings has four series connected batteries. Variations in the number of series and parallel batteries are common, depending on the application. In some cases, series battery strings are built up to obtain a target voltage (common examples are 12V, 24V, 48V, 100-600V, -1000V), and then parallel strings connect multiple(s) of the series battery strings together to obtain a target capacity of the battery system. A battery system will typically include the control electronics associated with the batteries in the battery system. For example, the battery system may include a battery management system (BMS), sensors linked to the BMS, and power conversion equipment such as a charger. A charger may be an inverter to convert AC to DC, a DC to DC converter or other device configured to provide power at a suitable level for the battery. The BMS may be configured to be in communication with thecharger. For example, a Controller Area Network (CAN) bus interface may be used. The communication may comprise a maximum charge and / or discharge limit.

[0083] Reference to battery strings herein should be understood to referto groups of batteries arranged in series and / or parallel. A string or group merely refers to one or more connected batteries. A group of batteries may be separable from the battery system as a group. The connections may be series, parallel, or mixed. For example, a battery system has a plurality of groups of batteries. The groups may be in parallel (e.g., eight batteries in parallel) or series (e.g. 8 batteries in series), or in a combination (e.g., 4 parallel groups of 2 batteries in series). The combination may be chosen based on power requirements.

[0084] Lead acid battery (LAB) battery systems may use battery management systems (BMS) to address LAB failure modes. In an unmanaged battery system each LAB is permanently connected to the battery system and is charged and / or discharged as a single unit. All LAB(s) in the battery system therefore act in substantial lockstep, ideally charging and discharging at the same time and having similar states of charge. However, these BMS methods do not provide sufficient performance or longevity for deep discharge high power battery systems or allow long lifetimes for the LABs used.

[0085] LABs may be single cells (for example 2 Volt cells) or multicell (for example 12V, 24V or 48V multicells made from 6, 12 or 24 2V cells). Multicell LABs are series strings connected internally (for example a 12V automotive LAB is actually six 2V cells connected in series). The internal connections typically prevent access and / or control over the individual cells within the LAB.

[0086] The discussed battery systems use multiple LABs connected in groups. Although discussed mainly in terms of LABs connected in parallel the use of LABs connected in series, or a combination of series and parallel is possible. One possible advantage (at least in part) of a parallel configuration in the battery system is it allows each LAB (or group of LABs) in the parallel configuration to be exposed to the same charging / discharging voltage at all times. There may be at least two parallel connected LABs or LAB strings, with the number of LABs or LAB strings adjusted depending on the application of the battery system. In some cases, eight LABs or groups of batteries may form the battery system. However, in a parallel arrangement each LAB or parallel group will normally charge / discharge at different amounts of capacity per cycle and can therefore rapidly diverge in state of charge and instantaneous powercontribution. The ability to integrate and segregate the LABs from the battery system, for example by switches, allows independent control of the LABs.

[0087] Figure 1 shows a battery system 1 comprising four LABs 20. The LABs are arranged in two parallel groups (strings) 17, with each group (string) 17 having two LABs 20. A battery system 1 may have a single group 17 or a plurality of groups. Each group 17 may comprise one or more LABs 20. Although shown as single batteries the LABs 20 may each comprise a plurality of batteries and / or a plurality of cells. Where batteries or LABs are discussed it should be understood that this may referto a single cell or multicell LAB, and that the battery or LAB may also or alternatively referto, or comprise, a plurality of connected LABs. For example, selecting which LAB 20 to charge may comprise selecting which group 17 of LABs 20 to charge, or which LAB 20 in a or each group of LABs 20 to charge or a combination of groups 17 and LABs 20 within groups 17. A battery group 17 (string) should be understood as referring to a single group (string) which forms part of a battery system 1 , or one of a plurality of groups 17 which combine to form a battery system 1. The use of groups of LABs allows larger battery systems to be managed more easily.

[0088] The BMS may be applied to a group of LABs in series. In some cases, the method of controlling the BMS would operate on the same principles as in the parallel examples described below. The BMS may provide independent integration and segregation of the LABs 20. However, the form of control, such as for example, by switching for integration and segregation would be modified to provide a bypass circuit when an LAB 20 is removed (as otherwise the single current path through the series string would be broken and no current would flow). In some cases, a bypass circuit is provided for each LAB 20 to be segregated, with switches segregating the LAB and inserting or connecting the bypass circuit. In some cases, extra LABs could be used to allow LABs to be replaced in the series group when segregated so as to maintain the battery system voltage. This may be because replacing a LAB with a bypass reduces the nominal voltage of the LABs in series. Alternatively, an inverter may be used to accommodate these voltage changes in the series group. For small-scale residential systems, the added cost of an inverter to control series groups and / or the complexity of this power control circuitry that may include an inverter for series groups is unlikely to be worthwhile due to the cost of the inverter. However, for larger installations where more energy and / or power is required, series groups become relevant to prevent charge and discharge currents becoming impractically large and therefore the use of an inverter may be worthwhile.

[0089] In an alternative, the BMS may be applied to one or more groups of LABs 20 arranged in parallel, with each group having one or more LABs. Having parallel groups allows a large output (discharge) current to be provided by integrating each of the groups, while allowing an input (charge) current to be provided to one or more of the segregated groups (or vice versa). The ability to change the current to or from each LAB allows the BMS to choose currents which, for example, can improve battery lifetimes.

[0090] A BMS for the battery system 1 is configured to segregate independent LABs (independent LABs including either individual LABs 20, or groups of LABs 17) from the battery system 1 and / or group of batteries 17 they are connected to. This enables independent management and / or control of independent LABs in the battery system 1 . Decoupling involves segregating independent LABs from the battery system 1 and / or allowing independent charging or discharging of the independent LABs without effecting the remaining independent LABs in the battery system 1. The integration / segregation (or isolation of independent LABs from the battery system 1) may be achieved, for example, through a physical connection and / or disconnection from the battery system 1, or by electrically segregating the independent LABs from the battery system. In each case the independent LABs 20 is unable to significantly charge (e.g. less than 0.01 C or below a threshold current of the battery system) or discharge through the battery system 1 while it is segregated. In some cases, the independent LABs are completely disconnected so that it is unable to charge or discharge any amount. The segregation is reversible so as to allow the independent LABs to be returned to the battery system 1 and allow full capacity operation of the battery system 1.

[0091] The LAB(s) 20 or group of LABs 17 may be considered independent where they are able to be separably segregated from the remaining LABs of the battery system 1. Alternatively, they may be termed individual LABs, although they may comprise a plurality of LABs within their connections to the battery system. In one example the BMS can segregate any one or more parallel batteries or groups of batteries from one another. For example, a set of parallel groups of batteries may each be segregated by being disconnected from the remaining parallel groups, or a set of series groups may each be bypassed.

[0092] In some cases, segregation requires additional control and / or switching in the BMS. Advantageously this may provide more options and / or flexibility when charging and / or discharging the LABs. Group-level operations may be separated from LAB specific operations. For example, if a particular or independent LAB requires maintenance the remainder of thegroup, or battery system, does not need to be exposed to the maintenance operation or any unnecessary charging or discharging required by the independent LAB. Segregation of an LAB from its group of LABs, or from other LABs, may be achieved through physical switching. Alternatively, segregation may be achieved by changing electrical parameters of the LAB. For example, increasing the apparent resistance and / or impedance of the LAB to the battery system means that the LAB will contribute insignificantly to the battery string and / or battery system. Although discussed as switches the integration and segregation may be performed by any suitable control device or plurality of control devices. In some cases, the control device(s), such as switch(es) are configured to controllably integrate and segregate the LABs independently based on signals from the BMS. For example, the control device or switch may be a variable resistor, a transistor, a relay, an integrated circuit, an electromechanical switch, a sliding switch, a rotary switch. Discussion of switches herein should be understood to refer to any suitable control device for selectively electrically integrating and segregating LABs.

[0093] In some cases, charging and / or discharging occurs when a group-level charge or discharge occurs. The BMS can choose which, and how many, LABs or groups of LABs in the battery system take part in a charge or discharge operation. LABs can be swapped in and / or out of a group or system as required to achieve the desired LAB or battery group or battery system characteristics. For example, adhering to a target charge or discharge rate for independent LABs or groups of LABs can be accommodated by integrating, segregating or connecting the appropriate number of LABs or groups of LABs to the battery system for presently available excess energy. For example, excess energy may be available from a solar power source. The BMS can integrate additional LABs into the battery system to charge using this excess energy. When there is an increased demand load from a home or energy user connected to the battery system, then the BMS can accommodate this increased energy use by integrating extra LABs to support this increased load, thereby discharging the LABs.

[0094] In some cases, the battery system is configured for home or residential energy management. This may include charging the LABs in the battery system from renewable and / or intermittent energy sources, such as wind and / or solar energy source, such as solar panels and / or wind turbines respectively. Maximising value of the LABs is provided where the majority of charging of the LABs comes from using excess renewable energy generated rather than using power from the grid to charge the LABs. However, on average solar, and other intermittent power sources are unpredictable as generally these power generation means relyon the weather and time of day. Therefore, for example, any excess power generated using solar generated power follows a "normal distribution" pattern as a function of the time of day (generation starts with very low power at around sunrise, rises through to peak generation at around noon and tapers off again toward zero power by evening). Generation at any moment in time is also variable due to clouds, temperature, time of year and other factors. Even with weather and / or predictive modelling the exact power production available is unpredictable. Similarly, household demand is variable depending on several factors such as number of users, time of day, power use dependent on household appliances and the like. Such use then contributes to the charging profile.

[0095] Therefore, in some cases, a BMS for a battery string or system may be configured to address any one or more of a plurality of objectives including, for example:Delivering the closest-to-ideal operating conditions to independent LABs within the string.Maximising the use of intermittent input energy (if connected) for charging the LABs in the battery string and / or selling any excess energy to the grid.Minimising the quantum and cost of energy bought from the grid to recharge the LABs in the battery string.Maximising the discharge energy throughput of the battery string during high-cost times (generally the evening period where demand is high).Maximising the stored charge in the battery string before maximum demand periods. Balancing the state of charge (SoC) of each of the batteries in the string.Alternative objectives may also be addressed in some cases.

[0096] In some cases, the BMS may also be directed to address effective usage of power from a power grid. For example, arbitrage-style usage where power may be purchased at a low price point to charge the battery system, and then, at a high price point, the battery system is used to support the household (or other load) or simply sold back to the grid. In some cases, this interacts with the intermittent power source (for example solar or wind). In some cases, this may be operated completely independently of a user. In some cases, the BMS will interact with external data sources to provide power cost details, such as data relating to a user(s) electricity pricing plan, time period, use and / or current price information and / or predicted price information. Such information and / or data can then be used to optimise the use of the LABs.

[0097] In some cases the BMS may address competing objectives. For example, the BMS may adjust charging or discharging based on battery lifetime, but may also consider the price of power, and / or the importance of charging or discharging. The BMS may be configured to reduce one objective to improve an alternative objective. For example, if the price of energy is high or extreme the BMS may decide to supply power, even with a potential risk of damage to the batteries (for example by increasing depth of discharge temporarily).Failure Modes

[0098] LAB types include, for example, prismatic, tubular, flooded, VRLA, absorbent glass mat (AGM), and / or bipolar batteries. Although these LAB types have different construction details, all such LABs can suffer from similar failure modes, particularly when the LABs are heavily discharged and / or undergo repeated cycling. Four possible failure modes of LABs are: positive active material degradation (PAM degradation), positive current collector corrosion (PCCC), separator dry out and negative active material sulphation (NAM sulphation).

[0099] PAM degradation occurs when lead dioxide (PbCy particles become disconnected from the positive electrode (the cathode during the discharge reaction). A possible explanation for PAM degradation is through damage to interconnecting necks in the electrode material. Figure 2 shows how lead dioxide on the positive electrode may be considered as an agglomerate of spheres (e.g., through the Kugelhaufen Model). In this model the convex particles such as spheres of lead dioxide are linked by concave particles, or necks of lead dioxide. Repeated cycling leads to a risk of dissolution and / or rupture of the necks, electrically isolating portions of the PAM within the electrode. To address this failure mode, or the electrode damage, corrective actions include: avoiding high negative discharge polarisations, avoiding deep depths of discharge, avoiding high charge polarisations at high state of charge, and avoiding frequent and / or excessive overcharge of the LAB, all of which can damage the necks of lead dioxide. Positive current collector corrosion (PCCC) occurs at the positive electrode (the anode during the charging reaction). The positive electrode's sub-structure (which may be referred to as the current collector or "grid") is typically formed from lead.

[0100] Figure 3 shows how, in one possible explanation, with every charging cycle, there may be corrosion. Corrosion occurs when converting some of the lead into lead oxides (PbO, PbCh). These lead oxides may be insulating and / or have a lower conductivity than lead and are additionally mechanically weaker. Over multiple cycles the quantum of lead oxides can increase until discharge capacity is minimal and / or structural failure occurs. To overcome thisissue, some manufacturers have increased the electrode thickness. However, this can lead to lower capacities at high discharge rates. As a result, this necessitates larger, heavier, and more expensive LABs to be built to serve a given application requirement(s) or at least to maintain the same requirements without any other improvements. In other LABs, such as in bipolar battery designs, this can require much thicker positive electrode current collectors leading to the same increased weight and cost disadvantages. Other ways battery manufacturers have tried to increase battery lifetimes is to increase the diameter and / or number of solder joints between adjacent positive and negative current collectors. Again, this leads to the same increased weight and cost disadvantages.

[0101] Separator dry-out is another failure mode. Separator dry-out is, especially problematic in an AGM battery and occurs during the charge cycle. This is because during charging an unavoidable side reaction is hydrolysis. This is the conversion of liquid water into hydrogen gas, H2, (produced at the negative electrode) and / or oxygen gas, O2, (produced at the positive electrode). In one possible explanation the conversion of liquid water to gaseous H2 and / or O2 represents a risk of mass-loss from the LAB, which must be carefully controlled. All created H2 must be lost from the LAB. A corresponding stochiometric equivalent of O2 must also be lost from the battery or be absorbed into the positive current collector through the PCCC failure mode). O2 may either be lost from the LAB or recombined at the negative electrode, depolarizing the electrode in the process. In some cases, an AGM battery aims to recombine as much O2 as possible, however 100% recombination is practically impossible, and so some level of loss occurs with every cycle. In some cases, the separator saturation levels can be estimated. For example, taking into consideration the age of the battery, environmental factors and history of use of the battery, such as the amp hour throughput of the same, along with other related factors. This estimate can be used by the controller to determine suitable charging characteristics, currents or thresholds as it is indicative of the health of the LAB.

[0102] In most conventional AGM battery designs, the mass (and associated liquid volume) loss occurs predominantly from the AGM separator. With continued cycling of the LAB the separator's liquid-filled fraction ("saturation") decreases, allowing easier passage of oxygen gas from the positive to negative electrode. Eventually so much oxygen reaches the negative electrode (this becomes the spontaneous direction) that there is insufficient charging potential to electrochemically charge the negative active materials. This causes end-of-life failure of the LAB. In some cases, alternative LAB structures, such as fabric structured electrodes(for example as referred to in WO2013133724A2 included herein by reference) delay separator dry out. Fabric structured electrodes allow control over the pore sizes in the LAB without compromising the structural properties of the active materials. This allows water loss to occur at the electrodes and the separator balances oxygen particles across the LAB.

[0103] NAM Sulphation occurs when a LAB is held at a partial state of charge. In one possible explanation, the lead sulphate in the negative active material (NAM) begins to convert into large PbSCU crystals - a process known as Ostwald Ripening (OR). As PbSO4 crystals grow, they become difficult and slow to charge. The OR process, if left unmanaged, will result in a negative electrode that cannot be fully recharged, therefore causing capacity loss. If left unchecked the LAB is unable to be recharged.Charging Methods

[0104] Methods to improve the performance of LABs are described. Improved performance of LAB systems enables broader use of LABs. Improvements may be achieved by physical LAB changes, such as improved electrodes, or through compression. For example, compression, such as provided in the AGM battery design and / or by reinforcing straps or tie rods through a bipolar battery design can also assist with reducing PAM degradation. In other cases, the control of the BMS can use one or more control techniques to reduce the failure modes. For example, through high positive electrode polarisation while charging at low states of charge, may reduce PAM neck degradation by encouraging deposition of PbCh at the neck sites. The methods described may be applied individually, but by applying one or more concurrently further improvement can be achieved.

[0105] Figure 4 shows a flow chart for determining charge or discharge states in a battery system. In state 180 the system is in a low voltage mode, where insufficient voltage is available from the charger, or a pre-charge is being performed. Once the charger bus (or battery system voltage) is at or above a determined threshold the BMS can operate. Until such time, the BMS enters the idle state 181. In the idle state 181 maintenance task(s) can be performed (on LABs or groups of LABs). In the idle state 181 the system will monitor for changes in voltage and can enter the charging or discharging states as required. If a suitable charging current is received (e.g. at least 0.05C) the BMS may enter the charging state. The action in the charging state 182 may depend on the current available. If the BMS determines sufficient current is available for charging, charging may begin. As discussed, the charging state 182 may determine how many LABs or groups to charge and / or how to charge them. This canbe based on available power and / or SoC or other battery characteristics. Charging may be at a constant current (typically at a low SoC) or constant voltage (typically at a high SoC). The constant current may be at a high current, at least initially to provide a positive overpotential. The constant current may be reduced after a period of charging, or a SoC threshold to allow more LABs to be charged concurrently and / or to reduce heating. If a discharge is requested and / or required, the system moves to state 183. Again, the number and rate of discharge may be controlled. Constant current or constant voltage discharge may be used dependent on the LAB SoC and / or required output power, for example. When a charge or discharge is complete, or no longer required the system returns to idle state 181. Various techniques for controlling the charging and discharging will now be described.

[0106] Example control techniques to improve the performance of a or each LAB or group of LABs in a battery system comprise: beginning charging cycles at an appropriate time; considering the characteristics of each battery string; and / or providing high current densities to low state of charge LABs. In some cases, high current densities at the start of charging encourages nucleation of lead dioxide within the PAM. In a possible explanation, this process of nucleation increases the likelihood of new PbC>2 particles budding from existing particles, creating a PAM structure with a greater number of small, interconnected particles and a more robust interconnecting system of necks. PAM structures consisting of smaller particles may have a subsequent reduction in electrical resistance, an increase in capacity with a reduced likelihood of the PAM breaking or the isolation / separation of areas of PAM and / or lead oxide within the positive electrode.

[0107] In some cases, for example where unlimited power is available, the high current densities may be achieved by simply selecting a large enough input current and applying this current to all of the LABs in the battery system. The input current may be above a threshold current. However, where intermittent or variable power sources are used it is not possible to arbitrarily select a suitable current. This situation exists when the variable or intermittent power is delivered, for example, by solar power. The key charging period is often at the start of the day when the LAB is at a low state of charge due to use of the LAB over the previous time period being the evening / night, however this may not correlate to there being sufficient power available to charge the LABs in the system. The BMS may address this problem by determining a number of LABs (or groups of LABs) in the battery system able to be charged with a or the available power source(s) (that may be variable). Using the independent control of the LABs viathe BMS, the BMS can determine a charge regime where only a determined number of LABs (or groups) in the string or system are charged. The remaining LABs can then be segregated from the battery system, and then integrated back in when necessary. The BMS can modify this charging regime in real time by constantly assessing for example the sufficiency of the power available, the SoC of the LABs, temperature and / or any other battery characteristics. Thus the charging regime may not be "a set and forget" or static configuration and has the ability to modify the same to accommodate any variations within the battery system as and when the variations occur.

[0108] An electrical measurement may be used to determine the number of LABs to be charged. For example, voltage and / or current measurements may be used. The electrical measurement can determine an available amount of power. The measurement may then be used to determine which, or how many, LABs to charge based on the amount of power provided to or by the charger. In some cases the available amount of power is limited by the charger. For example a battery system may have a 1 MWh power storage capacity, however is connected to a 250KWh charger (in some cases the battery system is instead limited by a maximum power draw or grid connection rating). The available power is therefore limited by the capacity of the charger, which in this case for example is a 250KWh charger. The BMS may use an electrical characteristic of the charger, such as charger power, to determine to charge the LABs and / or the number of LABs to be charged. In some cases there may be another component of the battery system limiting the maximum power (or current). For example, the cabling or connection can have a maximum power rating, or alternatively, the system may be limited by the electrical grid or the operator of the grid to not exceed a certain power limit. In this case the electrical characteristic of these component(s) may be used to determine which LABs and / or the number of LABs to be charged.

[0109] For example, a typical battery system will have a charger (inverter) with a power rating two to five times smaller than the battery system capacity. A 100 kWh battery would likely be fitted with an inverter rated between 20 and 50kW. This means the system, if charging all LABs concurrently would have a max possible charge current of 0.2-0.5C. Advantageously, the present system allows the LABs to be divided into a plurality of groups for charging, with cycling or rotation between the groups allowing higher charge currents to be applied to each group in turn.

[0110] In an example a current measurement from the power source(s) may be compared with a minimum current and / or current density for charging each LAB to determine the number of LABs which may be safely charged and / or which may be charged to extend the lifetime of the LABs. The minimum or threshold current and / or current density may be constant across all the LABs, or may vary, for instance based on LAB charge characteristics. In some cases, the BMS obtains or determines a charging threshold for each LAB. The charging threshold may represent a minimum charging current (or current density) for charging that LAB or groups of LABs. In some cases, the charging threshold is constant across the LABs.

[0111] As the input power available to the battery string increases, additional LABs may begin to be charged (i.e., additional LABs may be integrated into the battery string by the BMS). In some cases, the input power is monitored continuously and / or periodically to ensure appropriate charging. For example, by monitoring the input electrical characteristic, such as a current at a nominal voltage. Where there are extended periods of low power availability or where the charger has a power output rating below that required to achieve minimum charging power requirements across all batteries simultaneously, the BMS may switch the selected LABs to be charged. For example, once a first LAB has received a threshold State of Charge (SoC) recharge (for example at least about 0.2, 0.5, 1, 2, 3, 5, 10 or 20 percent increase in SoC or alternatively after a set time period, such as at least 10 seconds, 20 seconds, 30 seconds, 1 minute, 2 minutes, 5 minutes, 10 minutes, 15 minutes or up to 20 minutes or other increment in time for recharging), the BMS may switch the charging to a second LAB (or LABs) and so forth. This enables a charging current threshold (for example by a required minimum current density) to be met while at least partially balancing the SoC across the LABs. In some cases, characteristics of the LABs (or groups) are used to determine which LABs to charge first. For example, the strongest or weakest LABs may be charged first to ensure performance of the LAB(s) are maintained or to prevent damage. This rotation helps ensure a balanced SoC across the battery string or group and / or that a plurality of LABs are regularly charged.

[0112] The SoC or time of rotation may be selected or determined by the BMS to improve the LAB(s) performance. For example, through LAB rotation. If the LABs are being charged too quickly segregation can lead to a loss in performance through switching losses and LAB(s) impedances. Additionally, charging the LAB(s) too slowly or for long periods of time with a high charging current when the LAB(s) are at a low SoC can cause temperature increasesand increase differences in SoC between batteries. A rotation of 2% SoC, or between 1 % and 5% SoC balances these factors.

[0113] In some cases, the target charging current for the LAB(s) or groups of LAB(s) is variable. The target charging current may be dependent on the characteristics of each LAB or group. For example, the SoC, temperature, battery age, time since last refresh charge, time since last reconditioning, and recent usage history may affect the target charging current of each LAB. In some cases, when selecting which LAB (or group) to charge at low power charging availability, then the BMS may consider or match which LAB (or group) is able, or best suited, to charge based on that LAB(s) or groups of LAB(s) lowest target charging current.

[0114] In some cases, the charging threshold is a predefined threshold. The charging threshold may be a minimum charge rate forthe LAB. Charging a LAB above a minimum charge rate can achieve an overpotential at the positive electrode (i.e. an overpotential of the positive half-cell potential, or positive polarisation). Advantageously, a sufficiently high overpotential of the positive half-cell potential encourages the nucleation of new lead oxide particles at the positive electrode. At this predefined threshold, nucleation of new lead oxide particles increases the size of necks between particles (in contrast to growth of existing lead oxide particles) at low states of charge. The applicants have found that a positive electrode half-cell overpotential of about 200mV (or above 150mV, or above 175mV, or above 200mV, or between 150mV and 300mV, or between 175mV and 250mV) encourages nucleation. This overpotential is the difference between the positive half-cell potential during charge compared to the positive electrode's half-cell open circuit potential. Typically for a LAB, the positive electrode's half-cell open circuit potential is around 1.0V with respect to a Silver / Silver Sulfate reference electrode. This results in a desired positive electrode half-cell potential of 1.2 V with a 200 mV overpotential during charge. However, where a different reference electrode is used the overpotential may be relative to that different half-cell potential. For example, an alternative reference electrode is a standard Hydrogen reference electrode, the positive electrode's opencircuit potential may be approximately 1.68 V and therefore 200 mV of applied overpotential would measure approximately 1.88 V with respect to this standard hydrogen reference electrode. There are other alternative reference electrodes well known in the art which could equally be applied. In each case, the overpotential of relevance is taken as the difference in potential between the positive electrode half-cell open circuit potential and the positive electrode half-cell potential during charge.

[0115] The exact overpotential required may vary depending on various battery parameters. In some cases, a battery acid concentration at 100% SoC of at least 1.20 g / ml, or at least 1.21 g / ml, or at least 1.22 gm / ml or at least 1.23 gm / ml or at I.24 gm / ml, or at least 1 .25 g / ml, or at least 1 .26 g / ml, or at least 1 .27 g / ml, or at least 1 .28 g / ml is required to achieve the required overpotential. The temperature of charging may also affect the charging threshold. Higher temperatures may improve the charge acceptance properties of the battery, thereby reducing the overpotential required orto be achieved for a given charging current that would otherwise require higher charging currents. Additionally, there may be a balance required based on the operating temperatures that is dependent on the LAB(s) characteristics. In one example higher temperatures (for example greater than 30 degrees Celsius) may lower the sensitivity of the positive electrode overpotential to charging current and lead to higher charging current requirements than operation at room temperature, or 25 degrees Celsius or less. In some cases, lower temperatures (for example less than 10 degrees Celsius) may reduce the current required to achieve the required overpotential. The SoC of the LAB may also modify the overpotential response, with an LAB with a high SoC being easierto create an overpotential on. In some cases, the overpotential may be applied on or below a predetermined SoC.

[0116] The variation in overpotential of the positive half-cell electrode means that it may be advantageous to adjust the minimum threshold current dependent on one or more LAB characteristics. By controlling the threshold current dependent on the LAB characteristics, the BMS can provide the desirable positive half-cell electrode potential in a broad range of environments. For example, the system could monitor the positive half-cell electrode potential and adjust the minimum current threshold (or current applied to each LAB or group of LABs) to ensure a minimum positive half-cell electrode potential (e.g., 200mV) is achieved. However, it is difficult to monitor the voltage at the positive electrode. This is because of the typically destructive testing requirements of such a test on a LAB. In order to measure the positive electrode half-cell potential a reference electrode is inserted through the case of the battery to be placed in electrical and / or ionic contact with a target cell's electrolyte. The potential (voltage) difference can then be measured between the reference electrode and the target cell's positive terminal. This potential difference is the positive half-cell potential of the target cell.

[0117] Alternatively, the positive electrode half-cell potential can be estimated based on the measured cell or battery voltage and / or charge rate (e.g., (C)) of a LAB. It may be easierto measure an alternative electrical characteristic of the LAB and to determine or infer a positive half-cell electrode potential based on the electrical characteristic. For example, voltage measurements of the LAB can be used to calculate a charge polarisation, which can be used to infer a positive half-cell electrode potential. Figure 14 shows an example system for selecting or maintaining a desired overpotential on the positive half-cell electrode. An initial charging current is applied to the LAB(s), the charging potential of the cell can be measured directly (i.e. between the terminals of the LAB). The charge polarisation of the cell can then be calculated from the difference between the charging voltage and the open circuit voltage (potential). The charge polarisation of the cell includes polarisation at both the positive and negative electrodes. Therefore, the positive polarisation can be inferred by subtracting the estimate of the negative polarisation from the charge polarisation of the cell. In some cases, this positive polarisation is inferred through a percentage of overpotential typically on the positive electrode. This positive polarisation may be about 80% of the total charge polarisation at room temperature. In some cases, present battery conditions such as temperature, state of charge, state of health, and battery age will be taken into account when inferring the positive electrode polarisation. Characterisation of an LAB will allow the positive polarisation to be inferred.

[0118] Once calculated the measured positive polarisation can be compared to the minimum charging threshold (e.g., 200mV or other determined value). The BMS can then increase the current if the positive polarisation is below this charging threshold, or decrease the current if the positive polarisation is above the threshold. As shown in Figure 14 this calculation may be repeated during the charging process and / or in real time enabling the BMS to respond to variations in the battery system and / or power source during charging and / or discharging. This is because the positive half-cell electrode potential can be affected by temperature and SoC which may change the required current. In some cases, once determined, the charging current may be maintained over one, or a plurality of charge cycles, as the positive half-cell electrode potential may change relatively slowly based on battery history or state of health (SoH). In some cases the SoH of the battery may include an estimate of the separator saturation levels or degradation relating to separator dry-out. In some cases, one or more upper or lower limits are placed on the charging current. This may ensure a required level of charging occurs, or to prevent damage to the LABs. For example, the charging current may be limited to 0.5-1.5C. This should be sufficient to allow the desired polarisation.

[0119] Charge rates (and similarly discharge rates) may be expressed relative to the capacity of a LAB. This is commonly used because various effects on the LAB (such as lifetime) can depend on the charge rate relative to the size of a LAB. For example, a 20A charge / discharge rate may be damaging for a 2Ah (Amp Hour) LAB, but acceptable for a 20Ah LAB. However, the capacity of a LAB is also dependent on the charge / discharge rate. The Peukert effect explains that the slower a LAB is discharged the greater the dischargeable capacity of the LAB. This means that the charge / discharge rates may be specified relative to the time taken to discharge a LAB. A LAB can be considered discharged when its voltage falls below a voltage threshold. For example, for a 2V (single cell) LAB this may be 1.75V. Other common charge specifications include the C20 rate or capacity and C5 rate or capacity. The C20 rate means that the capacity is specified based on a current to discharge the LAB in 20 hours. For example, a C20 10OAh LAB would be designed to discharge at a constant current of 5A for 20 hours. However, at a C5 rate for the same 100 Ah LAB (discharging at 20 Amps) the capacity will appear lower - for example the LAB may fully discharge in 4 hours, discharging only 80Ah of capacity, which is less than the nominal 100Ah at C20. Herein, references to charging rate should be understood relative to the capacity discharged at the C5 rate. However, dependent on the use case of a particular system a C20 (common in automotive applications) may similarly be used.

[0120] Figure 5 shows a series of example relationships between half-cell potentials and charge rates of 0.125, 0.25, 0.5 and 1 C. A 1 C rate is a current suitable to charge or discharge the LAB in 1 hour (based on the C5 rate). For example, 20A for a 20Ah LAB. Figure 5 shows that at higher charge rates the potential or overpotential (relative to open circuit half-cell potential 500) at the positive electrode (also referred to as the positive half-cell potential) is increased. At 0.5C the potential is 100mV above the positive electrode's half-cell open circuit potential 500 of approx. 1 ,0V within the first 1 % of charge, while at 1 C the positive half-cell potential is 200mV above open-circuit half-cell potential 500 of approx. 1 ,0V within the first 1 % of charge. The 0.125C rate takes more than 15% SoC to reach even 100mV above open circuit potential of approx.1.0V.

[0121] Improved performance was shown for charging at or above 1 C in test battery conditions. However, some advantage may be achieved by charging at least 0.5C, at least 0.6C, at least 0.7C, at least 0.75C, at least 0.8C, at least 0.85C, or at least 0.9C dependent on the LAB configuration and / or characteristics. Testing has shown increased performance above each ofthese thresholds, with 1 C providing additional tolerance to battery parameters. As discussed above, battery characteristics may affect the desired charging rate. While greater charging rates (e.g. above 1 C) provide the positive overpotential, this needs to be balanced against the system requiring higher charge rates which may be difficult to provide (e.g., variable power supply requiring larger inverters and / or chargers), monitoring temperature and / or monitoring charging stress on the LABs. If left unmonitored, then such variables can lead to LAB damage. In some cases, a maximum charge rate of 1.2C, 1.3C, or 1.4C may be used to limit such LAB damage. In some cases, a maximum charge time at such high rates at low SoC may be implemented.

[0122] Figure 5 also shows that each charging curve requires a time period to reach the overpotential. This is visible in approximately the first percent of capacity returned. This time period to reach the overpotential when charging begins limits the speed and / or time at which the charging between groups of LABs should be rotated. The BMS wants to ensure the desired overpotential is reached during each charge. It has been found, that providing at least a 0.5%, 1 % or 2% increase in SoC for each charge period for each LAB or groups of LAB (or rotation) can achieve this.

[0123] Figure 15 shows the cell voltage (potential) forthe same battery as Figure 5. The cell voltage is greater than the positive half-cell potential because it includes the positive and negative potentials. The open cell potential 501 is shown at about 1.93V. Based on Figure 5 this means the negative half-cell potential is approximately 0.95V (1.93V - 0.98 (500)). The 1 C cell voltage at 1 C rises to about 2.2V, or about 0.3V above the open cell potential 501. Figure 5 shows about 0.2V is from the positive half-cell potential, meaning about 0.1V is on the negative half-cell potential. In some cases the cell voltage can be used to infer the positive half-cell potential, by assuming a similarly calculated ratio remains constant. The silver / silver sulfate electrode sets the base voltage in Figures 5 and 14. If a different reference electrode is used the absolute voltages may change. However, the overpotential to improve charging will stay constant relative to the absolute voltage. For example, a hydrogen electrode may have a positive half-cell voltage of 1.7V. Therefor for an overpotential target of 200mV (i.e. the same range as previously discussed) the overpotential would be 1.9V on the positive.

[0124] The disclosed BMS can control the groups of LABs in the battery system, enabling the LABs to be integrated and segregated in and out as required. Advantageously this allows control of which LABs (or groups) that receive the large charging rates (e.g. of greaterthan 0.5C). The disclosed BMS can select only to charge one or more of the groups of LABs within the battery system. By selecting a low number of LABs the current required to charge with the desired overpotential (for example, 1 C to achieve a 200mV overpotential) is reduced. This avoids an entire battery system being charged at high current (e.g., 1 C) which would require an input current equivalent to the capacity of the system (e.g. 20A for a 20Ah LAB). This current would require a large and reliable power source and power conversion equipment, such as optionally a charger (for example an inverter(s) or converter(s) or device configured to convert between DC and AC, AC and DC, or DC and DC) and / or components suitable for 20A.

[0125] For example, if there are eight LAB groups (assumed to have the same capacity in each group) arranged in parallel the system can charge any number of the LABs concurrently. The BMS may consider the input power (referred to as a current based on a set voltage) and decide how many LABs to charge (or if to charge no LABs). For example (assuming the group of batteries has a capacity of 2.5Ah), if 2.5A of current was available the system may choose to charge one group of batteries at 1 C. If 5A of current was available, the system may choose to charge two groups of batteries at 1 C. If 3A of current was available the system may choose to charge one group of batteries above 1 C, or to use the additional power elsewhere. This example avoids charging any of the groups at or below 1 C.

[0126] A further advantage of the BMS being able to integrate and / or segregate groups of batteries is that the charging can be switched between groups. In some cases, the BMS will monitor the LABs. Switching can reduce the temperature gained by any one of the groups due to the high charging currents. The switching, amongst other factors can also help to balance the SoC of each of the groups, and / or to avoid charge movement between the LABs. The rate of switching may be determined based on a threshold time, increased SoC as the BMS moves through its charging regime of the LABs within the system, and / or electrical characteristic of the LABs. The threshold time may be at least 5 seconds, at least 15 seconds, at least 30 seconds, at least 1 minute, at least 2 minutes, at least 5 minutes, at least 10 minutes, or at least 20 minutes. The threshold SoC may be at least 0.2%, at least 0.5%, at least 1 %, at least 2%, at least 3%, at least 4%, at least 5%, at least 10%, at least 15% or at least 20%. Decreasing the rate of switching can improve the reaction at the electrodes (due to the electrode capacitance preventing rapid changes in voltage) but is offset by the potential temperature increase and / or the unbalanced state of charge between LABs. In some cases, the LABs, or groups of LABs are selected in order of lowest SoC which would then be charged first.

[0127] The rotating of charging of the groups of LABs can also reduce the temperature of the battery system in whole or in part. Typically, high currents (e.g. above 0.5C or 1 C) are avoided because these cause heating of the LABs. This heat can damage the LABs, where such damage can be irrecoverable. However, by rotating or switching the groups of LABs being charged using the BMS, the temperature effects of high currents can be reduced and / or ameliorated. In some cases a temperature sensor is used to determine a temperature of the groups of LABs, and the temperature is used to determine one or more of: the number of LABs to charge, the frequency to charge the groups of LABs, or to adjust the charge rate of the groups of LABs. The ambient temperature may also be measured to determine the likely temperature response of LABs to a charge event and / or determine potential temperature loss from the LABs. Where the internal battery temperature is not directly able to be measured, an external battery temperature measurement may be used to infer an internal battery temperature, or used as a measure of battery temperature or likely temperature response to a charge event. In some cases the temperature of each group of LABs, or each LAB is monitored. However, it is also possible, where the groups are similar, for one group of LABs to be used to estimate temperature in the other groups. In some cases, where temperature may not be able to be measured, the rotation frequency or duty cycle is selected to ameliorate the effects of temperature. This may allow operation without temperature monitoring. In some instances, the LAB temperature increase may be delayed. For example, a high current charge may cause a temperature increase during the charge but may also cause the LAB to quickly increase in temperature in a following charge. Therefore, the BMS may estimate the effect of a future charge based on current battery temperature and / or previous battery charges as well as present, historical and predicted future ambient temperature.

[0128] For example, in an eight LAB group system the BMS may have sufficient power available to charge three LAB groups concurrently at a desired charge rate (e.g., 1 C). This means that each LAB is being charged in one of three time periods. The time period may be based on the length of time required to add the desired state of charge (SoC) to the battery, the LABs state of health (SoH), the LABs current temperature, or other LAB characteristics. If temperature increase is a potential problem, or if a sensor indicates a possible temperature rise, the number of time periods can be increased (or the number of LAB groups charged concurrently can be decreased). For example, in the eight LAB group system: if pairs of LAB groups are charged concurrently the battery system is charged in four groups, providing three rest periods betweeneach charging period for each pair. If each LAB group is charged independently then each group is being charged in one of eight time periods, with 7 equivalent rest periods until the next charge period. Increasing the number or time of rest periods between charge events for each group of LABs, reduces temperature gain.

[0129] Electing to charge fewer groups of batteries for temperature reasons (to look afterthe life of the battery) may be in conflict with absorbing all available power (i.e. the system charges at a lower rate than it otherwise could have). For example, using the previous example - the BMS may determine there is sufficient power available to charge two groups of batteries simultaneously, but that, if this was to occur, battery temperatures would rise too high. Therefore, the BMS may elect to reduce charge performance (total battery system charging will take more time) and charge only one group at a time at a lower duty cycle. Alternatively, or in combination, the charge rate may be reduced (e.g. 1 C to 0.8C, or by 20%, or other value). Temperature gain is typically proportional to current. By reducing the charge rate (or current) the temperature gained can be reduced. This may lead to avoiding high charge rates if the LAB temperature is high, even though the high charge rate may be beneficial to the positive electrode.

[0130] The battery temperature may be used to adjust a charging threshold, or used by the controller to change the charge of the LABs. Alternatively, or in combination, the amount of SoC added may be reduced. Previously a 2% SoC example has been used. However, adding a 2% SoC may increase LAB temperature too much. Therefore, the SoC added in each rotation may be reduced (i.e., to 1.5%, or from 3% to 2%). This may be advantageous where there is a long downtime between charges of any group of LABs. If the time between charges is relatively short there will be a limited recovery time between charges for the group and changing the SoC added will have a smaller effect. The change in LAB rotation may be referred to as changing a duty cycle of charging, changing a rest period between charges of each group of LABs, or changing the number of groups charged concurrently.

[0131] Figures 16, 18, 20 and 22 show example voltage and current curves over time for a 24Ah (C5 rate), 48V, bipolar LAB system. The battery system underwent four repeated discharge-recharge cycles, that differed with regards to the charging duty cycle used to return the battery back to 100% SoC. A constant discharge at C5 rate (4.8A) was used to discharge the battery from 100%SoC to approximately 20% SoC (approximately 80% depth of discharge (DoD)) in each case. This was determined by a 47.38V battery voltage being reached. A two-hour rest was provided before and after each charging sequence. In each example the charge cycle used a constant charging current of 1 C (24A) where the battery was charged up to 57.60V (2.40V / cell), at which point the battery was charged at constant voltage of 57.60 V (2.40V / cel I).

[0132] Figure 16 shows the first case where each of the eight groups of LABs (in this case arranged in parallel) were charged singularly. This provides a maximum rest period between charges for each of the group of LABs (i.e. the period in which each of the other LABs are charged). Figure 18 shows a second case where pairs of the eight groups of LABs were charged concurrently. Figure 20 shows a third case where fours of the eight groups of LABS were charged concurrently. Figure 22 shows a final case where all eight groups were charged concurrently. Expressed as duty cycles these comprise charging at 12.5%, 25%, 50% or 100% duty respectively. In each case twenty pulse-charge events were used, with individual charge pulses of fixed 180 second duration, equating to a maximum capacity per pulse of 5% SoC. This resulted in rest (open circuit) times between individual charge pulses of 1260 s (12.5 % duty), 540 s (25 % duty), 180 s (50 % duty) and 0 s (100 % duty). However, decreasing the duty cycle also increases the time required to charge the battery system, because more charging cycles (pulses) are required for the same SoC. For example, the time taken at 12.5 % duty cycle was 8 hours (12 to 2 Ohrs), while at 25 % duty cycle this reduced to 4 hours (32 to 36 hrs).

[0133] Figures 16, 18, 20 and 22 show a first period of constant current charging, and a second period of constant voltage, or at least reduced current charging (e.g. hours 14 to 24 of Figure 16). This is due to the groups of batteries no longer accepting a high current charge, and the system moving to a constant voltage charge. In some cases, a stepped current profile may be used, instead of the shown curve. At the conclusion of the 20 pulse charging events, a further four hours of constant voltage charging (over-charge) is performed in order to guarantee the battery system was returned to full charge (100 % SoC).

[0134] Figures 17, 19, 21 and 23 show the effect of the charging patterns (or duty cycles / rotations) on the battery systems (or group of LABs) temperature. Ambient (i.e. of the environment around the battery system), at the positive terminal, and the internal battery temperature are respectively shown. While the internal battery temperature is often the most relevant, the terminal temperatures are easier to measure. Across these figures, the ambient temperature remains relatively constant, however as the duty cycles increase (12.5-100%), then the internal and positive terminal temperatures all increase. This is especially shown in figures 20 to 23 where, as the duty cycle increases and approaches 100%, the temperature significantlyincreases. Therefore, higher duty cycles cause increased heating and the selection of the duty cycle, and / or monitoring the temperature can be used to determine a suitable duty cycle (charging rotation). The battery system may preferentially reduce a current or charging parameter to avoid temperature increase, or preempt temperature gain. This is because high temperatures may cause irreversible damage to the LABs.

[0135] Allowing a sufficiently large charging overpotential to occur at the positive electrode (i.e. the half-cell potential at the positive electrode) at the beginning of charging is particularly beneficial to the LAB(s). Charging overpotential encourage nucleation at the necks, and the nucleation produces a more robust PAM structure. In some cases, the overpotential only needs to be applied for a certain time period, or for a portion of charge added to the LAB (the portion of charge may be monitored by the SoC of that LAB). This can allow lower charge rates at higher states of charge of the LAB, or the charging of more LABs concurrently after the initial period. The overpotential may be applied for a first 1 %, 2%, 3%, 5%, 7%, 10%, 15%, 20%, 30%, 40% or 50% SoC of charge above a charging level. For battery performance the BMS may limit discharge to a base level. For example, the base level may be 15%, 20% or 25% SoC.

[0136] Figure 6 shows an example flow diagram for charging with constant current, however, it should be understood that analogous logic can be applied for constant power, and / or variable current or variable power control. The battery system for the flow diagram may comprise a group of eight LABs (or LAB groups) connected in parallel. Each of the LABs may be integrated to or segregated from the battery system. Each of the LABs has a capacity of 2.5Ahr, providing a total capacity of 20Ahr. The BMS limits the discharge of the LABs to a SoC of 20%. Other battery systems can use a similar process. Step 150 initiates charging by enabling charging of the LAB with the lowest SoC. Setting only the lowest LAB to discharge helps prevent charge flowing between the LABs. A rotation threshold is also set (for example, 2%). Step 151 then measures electrical characteristics of the battery system and / or charger. If, in Step 152, the SoC of the LABs is fully charged, the charging will stop (move to the idle state). If, in step 153, the SoC is sufficiently high (for example as indicated by a high battery voltage) the method of charging may change. Changing to, for example, a constant voltage charge method can improve battery lifetime. Alternatively, the constant current may be reduced to a lower current or alternatively, the current may be allowed to vary between defined upper and lower bounds. This may allow more LABs to be charged at once. Step 154 checks the charge current to the LABs or groups of LABs. Step 154 shows identification of four thresholds, less than 0.05C, lessthan 0.5C, greater than 1.1 C and between 0.5 and 1.1 C. As discussed above these thresholds may vary for a particular battery system.

[0137] If the charge current is within the desired range (e.g. 0.5 to 1.1 C) the system moves to step 157 and checks if rotation between LABs is required. If so, the LAB having gained a predetermined SoC, for example a 0.5%, or 1 % or 2% SoC, then that LAB is rotated to the next lowest SoC LAB. If the charge current is greater than 1 .1 C the system moves to step 155 and determines if a further battery can be charged at the same time. This will depend on the current available being sufficiently above 1 C. If the charge current is less than 0.5C the system will determine in step 156 if more than one LAB is being charged. If a single LAB (or group) is being charged, charging will pause until sufficient current is available. Alternatively, if there is substantially no charging current (less than 0.05C the system will move to the idle state 158.

[0138] This means that, during charging the BMS reviews the input current available and selects the number of batteries to charge. This can occur in real time, with the BMS having the ability to constantly monitor the battery system and the current inputs available. The BMS may have a charger (e.g., an inverter) able to supply a current of 6A. The BMS could therefore integrate and charge two of the LABs at 1 C. The additional 1A may be used to increase the charge rate or can be used elsewhere in the system. The BMS will then rotate the LABs being charged, so that after the first two LABs have been charged for example to increase the SoC by a nominal 2%, the next two lowest LABs can then be selected for charging again by increasing the SoC by a nominal 2%.

[0139] In this manner each of the LABs can be kept within a similar SoC range while being charged at a high current rate. This pulsed charging process at high current rate may continue until the SoC of all of the LABs is above 55% (so 35% SoC above the starting SoC). At this level, or the selected SoC, the charge rate can then be lowered, allowing more LABs to be charged concurrently, or allowing the LABs to use the excess current for charging. This lowered charge rate may be at a constant current, or at this threshold, or a higher threshold (e.g. 50, 60, 70, 80 or 90% dependent on temperature and charge currents, battery characteristics etc.), may move to a constant voltage, due to LAB limits. Where the charging source is variable the number of LABs to be charged may vary depending on the available power. For example, no LABs may be charged until sufficient power is available to charge the LABs at the minimum charge rate, or is able to sustain the charging threshold, such as for example 1 C for two LABs.A parallel configuration may be useful here to allow the individual charging of LABs, whilst discharging all the LABs concurrently.

[0140] In some cases, the desired charge current will vary with SoC of the LABs or groups of LABs. The high current charging described above is advantageous when charging from low SoC. However, once a threshold SoC has been reached the LABs may advantageously be charged at a lower charge rate. This may be a lower constant current or power rate, or alternatively, controlled at a constant voltage. The use of a constant voltage improves the battery life because the charge current is limited by the charge acceptance of the LABs. For example, above a 60%, 65%, 70%, 75% or 80% SoC the LABs (or groups) may be charged at the constant voltage rate. Figure 4 shows a test for this in step 153. Using a lower charge current allows more LABs (or groups) to be charged concurrently, or to make use of power available above the 1 C charge rate. For example, between a 20%, 30%, 40%, 50%, 60%, 70% or 80% SoC threshold and the constant voltage threshold the LABs may be charged at a reduced constant current rate (relative to the overpotential current rate). Again, a rotation (e.g. 1 %, 1 .5%, 2%, 5% or a time based rotation) may be used to balance SoC between LABs.

[0141] Figure 7 shows an example flow diagram for charging at constant voltage. This may be implemented separately to (i.e. after all LABs reach a threshold SoC) or concurrently with the system of Figure 4. For example, some LABs may be charged with constant current while the higher SoC batteries are charged with constant voltage. Step 160 enables only the lowest SoC LAB to discharge, to present current flows between the LABs or groups. Step 161 receives one or more measurements (for example a charger set point) and determines in step 162 if the charge is complete (SoC greater than or equal to 100% for all batteries). Any fully charged LABs can be moved to the idle state. In step 163 the BMS checks the LABs are healthy by checking they are received charge while having voltages below their expected maximum. LABs failing this test can be selected for calibration and / or maintenance. Step 163 stops charging of any batteries with 100% SoC, to avoid unnecessary overcharge.

[0142] In some cases, each of the LABs in a or each battery string can be regularly (e.g., daily, monthly) charged to substantially full capacity. This may be a first target LAB SoC. The substantially full capacity may be a capacity of between 95% and 101 or 105% SoC. The ability to fully charge the LABs may depend, for example, on the presence of enough input power, especially when dependent on intermittent generation such as solar power. Charging to this first SoC level reduces failure of the LAB(s) due to separator dryout while maximising batterySoC. In some cases, the charging voltage is also controlled, because charging at high voltages can be particularly damaging, especially at higher SoC's. In some cases, the BMS prevents charging of at least one LAB (for example by segregating the LAB) when the charging voltage is too high, or current (at a given voltage) falls below a threshold or reduces the charging voltage once a desired SoC is reached. This may lower positive electrode charging over potentials. For example, the charging voltage may be reduced above, 50%, above 55%, above 60%, above 65%, above 70%, above 75%, above 80%, above 85%, above 90%, or above 95%.

[0143] In some cases, the SoC is monitored electrically, for example with a coulomb counter for each LAB. The use of a coulomb counter, or other means of tracking the charge added and / or removed from the LAB is that the SoC of the LAB can be determined relatively accurately. In some cases, a periodic charge may be performed to reset the coulomb count and adjust for any loss in accuracy. The ability to track the SoC closely makes cycling battery charging (or pulsing charging between batteries) easier - as it is difficult to quickly ascertain SoC from voltage characteristics alone. This allows the BMS to pulse charge LABs to maintain a balanced SoC in each of the LABs or groups of LABs, allowing high charge rates to be used as previously discussed.Discharge Methods

[0144] It has been found that in LABs in a battery system the positive active material (PAM) may degrade when discharge polarisation becomes too high during discharge. This action can discharge the PbC>2 (lead dioxide) within the concave regions of the PAM particle network and break the lead dioxide necks, if present. In some cases, the BMS will monitor the discharge rate or a required discharge rate of the LABs and modify the discharge of the LABs based on the determined charge characteristics of one or more of the LABs.

[0145] In some cases, the charge characteristic may comprise a SoC of each of the LABs. If at least one of the LABs has a SoC lower than the remaining LABs (or at a threshold below the state of charge of the remaining LABs) it may be prevented from discharging, for example by segregating LABs (or disconnecting) from the battery string using the BMS switches or other control device. The LAB may be segregated (for example by being switched out) for a predetermined and / or calculated period of time and / or until the average SoC of the remaining LABs has reached the SoC of the switched-out LAB and / or the voltage of the discharging battery string becomes compatible with the disconnected LAB(s). In some cases, this allows the state of charge of all the LABs to be maintained within plus or minus 10%, plus or minus 7%,plus or minus 5%, plus or minus 4%, plus or minus 3%, plus or minus 2.5%, plus or minus 2%, plus or minus 1.5%, plus or minus 1 %, plus or minus 0.5%, plus or minus 0.25%, plus or minus 0.2%, plus or minus 0.15%, plus or minus 0.1 %.

[0146] The SoC of the LABs may be substantially balanced during each action of the BMS 10, if possible. This enables maximum power to be drawn from the string by integrating or connecting all of the LABs. If one of the LABs has a significantly different SoC when it is integrated to the string this may cause unnecessary and / or uncontrolled charging and / or discharging within the battery string with the potential to therefore reduce battery lifetimes. The SoC may be balanced by monitoring the charge in each battery and ensuring the battery system has a plurality of batteries within a target range of SoC, as detailed in the previous paragraph, and with reference to the rotation during charging in the examples above. This may be considered for any action, including charging and discharging. For example, when discharge begins the highest SoC LAB may be used first, until it reaches substantially the same SoC as the second highest SoC LAB. In some cases, grid power may be used to equalise the SoC of the LABs. In some cases, LABs may be segregated from the SoC balancing - for instance if the LAB is due to have maintenance performed, or an overcharge. In some cases, the SoC balancing is prioritised over charging or discharging of the LABs. For example, power may be exported to the grid instead of being used for charging, until the SoC of the LABs has been substantially balanced. In some cases, additional LABs may be used in the battery system to provide full power when some LABs are segregated.

[0147] In some cases, the charge characteristic may comprise an electrical measurement of each of the LABs. In some cases, the charge characteristic signifies an over discharge of a LAB. For example, a voltage measurement may indicate a sudden drop in voltage and / or current (potentially signifying the depletion of at least one cell within the LAB) or a relatively low battery voltage. For example, the voltage measurement may be an open circuit voltage of less than 1 ,9V per cell, or 45.6V on a nominal 48V LAB. The electrical measurement may, alternatively, or in combination with the voltage measurement, be one or more of be an AC signal impedance at a specific frequency (e.g., 1 kHz), or DC pulse perturbations to assess apparent DC resistance. This electrical measurement may be used to identify LAB(s) which require maintenance during the discharge cycling. In some cases, the LAB(s) are prevented from discharging further. In some cases, the LABs may be flagged or recorded as requiring external maintenance and / or flagged to have a rigorous overcharge during the next chargingevent. In some cases, the maintenance and / or overcharge is configured to refresh all of the cells within the LAB to a high SoC, resulting in a high battery SoC.

[0148] In some cases, the BMS is configured to concurrently discharge as many groups of LABs and / or LABs as possible during the discharge cycle. This minimises the discharge current density experienced by all of the LABs because the charge is drawn from each of the LABs. In some cases, this allows the BMS to reduce the discharge current density to below 160A / m2 of battery electrode to assist with extending the battery lifetime. In some cases, the use of all LABs at the same time is avoided, as if the LABs have different SoCs there may be undesirable energy movement between the LABs. In this case the BMS may monitor the SoC of each of the LABs and integrate and / or segregate LABs from the battery string to ensure the SoC remains substantially constant, as described above.

[0149] Figure 8 shows an example flow diagram for control of the discharge. Step 170 determines which LABs are above a minimal SoC threshold, for example 20%. This prevents over-discharge of the LABs. Enabling charging for only the highest SoC LAB prevents charge flowing to from high SoC batteries to low SoC batteries. Step 171 received measurements of one or more charging characteristics. Step 172 prevents discharge of small currents (for example, below 0.05C). This is a safety threshold which prevents over discharge of the battery in the instance where the BMS's SoC counter is inaccurate, orthe battery is an unexpected state and is incapable of delivering significant current. As described, the system may also determine how many LABs should be discharged concurrently. In some cases, all, or substantially all of the LABs are discharged together to reduce the discharge rate The system may also implement, in step 173 a check on LAB performance. If the LAB voltage is at or below a minimum threshold and the discharge current is low (below 0.05C) but the SoC is greater than an empty LAB (e.g. >20%) the LAB may be disabled and maintenance performed 175. This prevents damage to underperforming LABs. Otherwise, in a normal discharge, discharge is stopped 174 at a base SoC (for example 20%)Maintenance

[0150] In some cases, problems may be detected in LABs in the battery system during charging or discharging cycles. While these may be addressed through the charging and discharging cycles in some cases it is advantageous to provide separate maintenance cycles for poorly performing LABs.

[0151] In some cases, the BMS may determine that the capacity of an LAB or LAB group has fallen below a threshold level, for example the capacity has reduced by 10% or more. In some cases, by discharging the LAB to a very low SoC (e.g., less than 25%, less than 20% SoC, less than 10% SoC, less than 5% SoC, or substantially below 0% SoC, or below a battery voltage threshold such as less than 1 .75 V / cell, (described previously) at very low discharge rates (e.g., 10A / m2of electrode). In some cases, this process, or similar processes may increase the concentration of lead ions in solution at a discharge rate that does not induce the dissolution of lead dioxide necks on the positive electrode. While discharge proceeds, and further, when the LAB is subsequently charged, the lead ions will recrystallize on the neck zones. This increases neck strength, and reduces the overall resistance of the positive electrode, returning any lost capacity in some cases.

[0152] In some cases, the BMS is configured to periodically overcharge the LABs. The overcharge may be to 105%- 120% SoC or above 101 % SoC, above 105% SoC, or between 101 % and 120% SoC. In some cases, this may robustly avoid NAM sulphation, however, the process can encourage separator dry-out. In some cases, the periodic overcharge occurs less frequently than regular charging. This frequency may attempt to strike a balancing act between capacity loss via NAM sulphation and capacity loss / battery failure via desaturation of the separator via hydrolysis / water loss. Similarly, both PAM degradation and positive current collector corrosion may be promoted during overcharge. Therefore, there may be an additional risk if any LAB is overcharged regularly leading to reduced battery lifetime. This cure for NAM sulphation may, therefore advance at least the other LAB failure modes described. Advantageously the BMS may address this problem by allowing LABs in the battery system to be independently overcharged. This may avoid unnecessary overcharging of the other LABs (e.g., when only a single LAB is problematic). Limiting the number of overcharges of each LAB in the battery system (or for individual LABs in a group of LABs) increases performance and lifetime of each LAB and the battery system.

[0153] In some cases, regular charging to a first target LAB SoC (e.g., to 80 - 105% SoC or 85-105% SoC, 90-105% SoC or 90% to 100% SoC) may occur substantially daily while overcharge to the second, higher, LAB SoC (to an overcharge to 105% to 120% SoC equivalent, or 105% to 140% SoC equivalent - i.e., a 5-40% overcharge of the LAB, or 5-40% of the full battery SoC) may occur for example, only substantially monthly. In some cases, for example where not enough power is available over the course of a day, the regular charging may notreach the target LAB SoC. It will be understood that the overcharge is expressed in terms of SoC for readability. Although SoC technically does not refer to overcharged states a 120% SoC can be understood as a 20% overcharge, for example.

[0154] The actual periodicity of each charge type may depend on any one or more characteristics of the battery system such as, the system application or use, the charging power source, and the types of LABs used. The periodicity of the overcharge may be different for different LABs in the same battery system, or the or each group of batteries of the battery system, and the charge characteristics of each of the LABs. For example, the BMS may flag or identify particular LABs which show potential NAM sulphation. In some cases, if a LAB has been flagged as being at low SoC, then that independent LAB will receive an overcharge (105% to 120% SoC) - but other LABs in the battery system that have not been so flagged will avoid this overcharge, to therefore avoid unnecessary potential damage to the other LABs in the battery system. In some cases, the number of overcharges may be limited in a period (e.g., to 52 times per year), or recorded to determine underperforming LABs. In some cases, the BMS selects, when charging the LABs, which LAB requires charging to the second SoC based on the charge characteristics of each LAB.BMS Controller

[0155] Figure 9 shows a BMS 10 for a battery system in a residential location such as a house 15. The house 15 is connected to a power source, shown as grid 13. Alternatively, or additionally, the house 15 may be connected to local energy source. The local energy source may be an intermittent energy source such as a wind generator and or solar generator. Alternative power sources may also be used. The BMS 10 is connected to the house 15 by an inverter 16, configured to convert the DC energy stored in the LABs into AC energy for the house 15. In some cases, the inverter 16 may form part of the BMS 10, or at least receive control signals 26 from the BMS 10. The inverter 16 is configured to connect the battery system 1 to one or more AC power networks, such as the power grid and / or the household 15.

[0156] The BMS 10 comprises a controller 1 1 configured to control the operation of the BMS 10. The controller 1 1 may receive data from, or be in connection with, one or more sensors 19 and be configured to control one or more switches 18 of the BMS 10. In some cases, the controller 11 comprises a memory configured to store data on the operation of the BMS 10 and / or the LABs 20. The data may comprise performance data of the LABs 20, such as Amp hour throughput, SoC estimation, Voltage vs SoC estimation, temperature, and age. In somecases, the data comprises historical data. The controller 1 1 may also control the inverter, for example to set charge or discharge currents to the battery system 17.

[0157] The battery system 1 comprises a plurality of LABs 20, which may be referred to as a battery string or group of batteries. The battery system has at least two LABs 20, with the number of LABs configured dependent on the capacity and / or power required. The LABs 20 are connected in parallel. The battery system 1 is configured so that each of the LABs 20 (or each group of LABs 17) is independently controllable by the BMS 10. This means that each LAB 20 is configured to be independently reversibly connectable or integratable / segregatable to / from the battery system 1. Figure 1 shows two LABs 20 connected in parallel. As described in some cases each LAB 20 comprises a single cell LAB, a multicell LAB or a group of LABs. In alternative arrangements further LABs may be included in parallel and / or series strings.

[0158] Control devices, such as switches 18 may be used to electrically connect and electrically segregate or isolate the LABs 20 while allowing the remaining LABs to charge and / or discharge. Two MOSFET switches are shown in Figure 9, however alternative configurations or control devices may be used to provide a suitable switch 18. Two back-to-back switches may be used to enable bidirectional power switching. An integrated diode and and / or an ideal diode controller may enable power transfer with low losses. For example, alternative electronics may comprise physical breakers, increasing the impedance of the independent parallel circuit, among other possibilities. The switches 18 are controlled by the controller 1 1 , for example by control lines 28. Individual or independent control allows the LABs 20 to be managed independently. By managing the LABs 20 independently the characteristics of each LAB 20 can be considered when making charging decisions. Surprisingly this dramatically increases the lifetime and / or performance of the battery string 17. In some cases, because of the independent management of the LABs 20 the SoC of each of the LABs must also be monitored and balanced to ensure the battery string 17 can operate efficiently when discharging multiple LABs at once.

[0159] The BMS 10 comprises sensors 19 for monitoring the LABs 20. The sensors 19 may be electrical sensors such as current and voltage sensors configured to measure electrical characteristics of the LABs 20, such as currents, voltages, resistances, or combinations of these. The current and voltage sensors may be configured to determine the SoC of the LAB, for example by coulomb counting during charge and discharge of the LAB 20. In some cases, the sensor(s) directly measure SoC and / or comprise a current counter. Alternative techniques maybe used to determine the SoC. Additional sensors 19 may also be used to measure electrical, thermal and / or other characteristics of the LAB. The controller 11 may use the sensor measurements to determine suitable charging methods for the LABs. The controller may be connected to the LABs 20 through signal lines 29.

[0160] In some cases, the controller 1 1 may be configured to assess periodically and / or continuously the following BMS 10 characteristics, for example:Battery charging priority (e.g., which LAB(s) 20 should receive priority for being charged when electricity is available);Charging variables (e.g., max voltage, max current, duration) per LAB 20 from low SoC to high SoC;Sequence of battery charging (e.g., which LABs 20 should enter and exit the charging sequence at which time);Which LABs 20 are to participate in any discharge event and / or require scheduled maintenance.

[0161] Figure 10 shows a possible layout of the BMS controlling a battery system 1 comprising eight parallel groups of batteries 17, each group having one LAB 20. Again, the LABs may comprise single cells, multicell or strings of LABs. The LABs 20 of Figure 10 are connected in parallel, although alternative series or series and parallel arrangements are possible. Power (e.g., from solar panels, wind generation and / or a grid connection) is received at input 30, with switches 18 being used to control which of the eight LABs 20 are charging and / or discharging. Current sensors 39 and voltage sensors 38 provide electrical measurements of the charging and / or discharging currents to allow the LAB 20 state of charge (SoC) to be determined. The current sensors 39, voltage sensors 38 and switches 18 are monitored or controlled by controller 1 1 , for example through control lines 28.

[0162] In one example the battery system 1 comprising battery groups 17 operates as an Energy Storage System (ESS), with the BMS controlling the operation of the battery string 17. A parallel string is used in most applications (for example, residential battery, commercial, industrial, and grid) so that the battery system has a capacity significantly greater than the capacity of an independent LAB 20. For instance, the example of Figures 9and 10 may be configured for eight 2.5kWh LABs 20, providing a 20kWh battery system 1. A 5kW or 7Kw inverter may be provided, allowing a simultaneous charge rate of 0.33C to 0.41 C. The BMS may monitor the LABs 20 in the battery system 1 (e.g., using the sensors 38, 39) to improve theperformance and / or lifetime of the battery system 1 and / or each of the LABs 20. The size of the battery system may be adjusted depending on power needs. For example, an industrial system may be 500kWh to 100kWh with a 10-50kW inverter. This may have 20-50 LABs and a simultaneous charge rate of 0.2C to 0.5C. For example, a containerised system may have 500kWh with a 100 to 250 to 500kW inverter. The containerised system may have 220 to 500 LABs and be able to simultaneously charge all the LABs at 0.2C to 1 C. Reducing the inverter size, by using the described system and methods can reduce the size or cost of the systems.

[0163] Figure 11 shows an example flow chart for the processing and control performed by the BMS 10. The BMS 10 may have one or more power requirement inputs 40. The power requirement inputs may comprise an estimated external or available power generation 41, a power flow 42 from the LABs 20 and a demand power from, for example the household 15. The power inputs 40 are configured to allow the controller 11 of the BMS 10 to make a charging decision 70 - to decide if charging or discharging the LABs 20 is required and / or possible. In some cases, the power input(s) 40 are provided by a current drawn or provided to or from inverter 16. The controller 11 may be configured to determine if the desired current is available to / from the inverter 16. In some cases, the controller 11 is configured to control the inverter to alter the power settings.

[0164] The BMS 10 may have a plurality of inputs for determining battery status 50, such as if the, or each, LAB is able to charge or discharge as requested by the controller or for determining the protection needed to increase the lifetime of the LAB. The battery status 50 may determine maximum and / or minimum rates of discharge 51 and / or charge 52 of each of the LABs, for example in order to protect the electrodes of independent LABs. The battery status 50 may also determine the battery polarisation 53, which, in part, indicates the status of the lead dioxide on the PAM or NAM and / or may indicate the health of the electrode(s). The battery status 50 may also use or determine the SoC 54 of each LAB so as to determine which, if any LABs can be charged and or discharged optimally and safely. A temperature input 55 may be used to determine battery performance and / or to contextualise or modify the other inputs. For example, the current / voltage / resistance / impedance of a LAB may be temperature dependent.

[0165] The BMS 10 may have a plurality of inputs for determining battery life 60. These may include the state of charge 54, with a low, or lower SoC potentially indicating the LAB 20 is not performing as well as the other LABs 20. The number of charging cycles 62 may indicatewhether an overcharge is required or desired to reduce NAM sulphation. The history or prior performance 63 of the LAB 20 may also indicate battery life 60, for example if a LAB 20 is charging slowly or failing to charge to a full SoC this may require that particular LAB 20 to undergo a slow discharge to refresh or repair the LAB 20. In some cases, the length of time since the previous overcharge of the battery or another electrical characteristic of the battery may alternatively be used. In some cases, an independent LAB 20 is overcharged at any one time. Alternatively, a subset, or all, of the LABs 20 can be overcharged concurrently, if required for all the LABs 20 in the subset or group 17. While discussed herein as an overcharge, depending on the nature of the LABs the charge may simply be sufficient SoC to address the NAM degradation issue.

[0166] The BMS 10 may use at least one of the power requirements 40 and battery status 50 to determine whether to charge any of the LABs 20. For example, if there is energy available and the LABs 20 have low SoC 54 the BMS 10 may determine it is suitable to charge the LABs 20. However, the BMS may undertake further checks, such as the number of LABs 20 to charge 71, and which LABs to charge. For example, where limited power generation 41 is available (such as in the morning for a solar energy source) the BMS 10 may determine that it is possible to charge the LABs 20, but the battery status 50 indicates that a limited number of LABs should be charged as a higher charging current will maintain the health of the electrodes when charging from low SoCs. In some cases, this may mean one or two of the LABs 20 are charged.

[0167] In some cases, the BMS may also determine which LABs to charge 72. The BMS 10 may rotate which LABs 20 are charged dependent on time and / or SoC for example, to balance the charge in each LAB 20. As the generated power increases further LABs 20 may be charged concurrently. The target charging current may be different for different LABs, for example based on prior performance 60. For example, characteristics such as at least one of: SoC 54, temperature 55, number of charging cycles 62, prior performance 63 (any one or more of age, time since last refresh charge, time since last reconditioning, or recent usage history of each LAB 20) may be considered. These characteristics may be considered to select a charge rate above the 1 C rate discussed previously, or used to select a different charge rate to improve the LAB performance. Charging a plurality of the LABs concurrently increases the speed at which the LABs 20 can be charged and is straightforward during normal operation (i.e. during daily charge). Although described with respect to LABs 20 in a single group 17 of a batterysystem the calculations may also be applied to LABs in a plurality of groups 17 within a battery system, or the LAB 20 may represent a plurality of connected LABs (i.e. a further string). In some cases, a BMS may operate at multiple levels of a battery pack - i.e. operating at an individual LAB level and for groups of LABs 17 level (where for example a plurality of groups of series batteries are all arranged in parallel).

[0168] During charging and / or discharging cycles the BMS 10 may determine that one or more of the LABs 20 (or groups 17) are operating below a target performance and / or are substantively lagging behind the other LABs 20 of the battery system. Based on this determination the BMS 10 may schedule battery maintenance 73. The battery maintenance 73 may be carried out by the BMS 10 in a later charging or discharging cycle, or alternatively may be flagged to a user and / or operator to action by an indicator and / or an alert. For example, if a LAB 20 is not reaching the SoC of the other LABs 20 in the battery system it may be scheduled to have a deep discharge. The deep discharge may comprise a discharge to a low SoC (for example <25%) at low rates (for example <0.5C) followed by a recharge at high charging rates. The recharge may take place within, for example 4 hours. Other maintenance charges may be used to attempt to improve battery performance. The LAB(s) 20 may be segregated from the battery system 1 while waiting for maintenance.

[0169] In a further example the BMS 10 may monitor the SoC 54 when charging at least one LAB and decide whetherto keep charging 70 each LAB 20 based on the SoC 54. This allows the BMS 10 to control the occurrence and level of overcharge of each LAB 20, as charging past approximately 95-100% SoC can be damaging on the LAB if carried out uncontrollably, especially at high voltages. To address this, charging 70 may be reduced once a SoC threshold is reached, charging may be reduced by reducing the current and / or voltage (e.g., to < 150mV above open circuit voltage) provided to at least the LABs 20 having the high SoC. In some cases, this is achieved by BMS 10 signalling the inverter 16 to reduce the charge voltage setpoint. In some cases, the BMS 10 may switch out or segregate LABs 20 with high SoC so as all the LABs 20 reach the threshold SoC before the inverter 16 is signalled.

[0170] In some cases, the independent control of LABs 20 by the BMS 10 is used to limit any overcharge at a per LAB level, instead of having to overcharge the entire group or the battery system 1. This means that each LAB 20 (or group of LABs) can be charged independently to an ideal level, avoiding the need to excessively overcharge some LABs 20 within the battery system that have different SoCs. This avoids blanket overcharging all theLABs in order to satisfy the overcharge requirements of a single LAB 20 within the system. This additionally, may reduce unnecessary mass loss in the LABs 20 which reach full charge first, assisting, among other failure modes, a reduction of separator dry-out. This may be achieved by monitoring independent LAB 20 SoC and preventing charging of each LAB 20 as it reaches the overcharge threshold. The overcharge threshold may be set between 95-105% SoC, or between 95 and 101 % of SoC, or similar values. The desired threshold may depend on the type of LAB 20 used and / or the desired lifetime or performance.

[0171] In some cases, the BMS 10 uses the independent control of the LABs 20 to apply a low discharge limit to the LABs 20. The BMS 10 may monitor the SoC of each of the LABs 20. When the SoC of a LAB 20 is at or below a lower threshold (for example, 10%, 15%, 20%, 25%, 30%, 35%, 40% SoC) the LAB 20 may be segregated from the battery string 17 to prevent further discharge. Discharge below this lower threshold, particularly if regular or over many cycles may increase the chances of discharging the necks of PAM active material structure. In some cases, the discharge rate and / or current densities may be monitored and / or limited by the BMS to allow further discharge (i.e., at or below the threshold). In some cases, the BMS 10 controls the inverter 16 to limit and / or modify the discharge current. A lower discharge rate may reduce PAM degradation. This avoids a trade-off between a discharge threshold based on the worst battery or causing damage to one or more of the LABs 20 by over discharge.

[0172] In some cases, the BMS 10 provides a periodic refresh charge, where the LAB(s) 20 are charged to a higher threshold level or overcharge. This threshold may be at least 101 %, at least 105%, at least 1 10%, at least 1 15%, at least 120%, at least 140%, or up to 150%. This may be performed on a scheduled basis (e.g. monthly or weekly) and / or on an as required basis when LAB(s) are detected to fall below threshold performance requirements. In some cases, a significant overcharge aims to refresh the battery electrodes by recovering sulfation effects, particularly in the negative electrode, but should not be performed on every cycle, so as to mitigate separator dryout. Because the BMS 10 has independent control of the LABs 20 or groups 17 it is able to perform this refresh charge without causing unnecessary damage to all the LABs 20. In some cases, the refresh charge, is triggered by a measurement of the LAB 20 and / or battery performance.

[0173] In some cases, the BMS 10 also controls the discharge 70 based on the battery status 50 and power requirements 40. For example, it may be generally advantageous to minimise discharge current densities to protect the positive and / or negative electrodes. Thismay be achieved in the BMS 10 by discharging as many LABs 20 as possible. However, the battery status 50 may indicate that some LABs 20 should not be included in the discharge within the remaining battery system because, for example, they have a low SoC (having not been recharged properly, for instance), have been flagged for battery maintenance, or they are out of sync with the remaining battery system (which may cause power flows within the battery system).Example Day of Operation

[0174] Figure 12 shows an example operation of the BMS 10 over the course of the morning and noon parts of a day. The BMS controls a battery system with a single parallel battery string 17 (e.g. a group of eight batteries arranged in parallel). The day is broken into five uneven sections, Morning 100, Midday 101 , Afternoon 102, Evening 103 and Overnight 104 (see Figure 13). The situation is merely an example, and a different battery system, BMS 10 settings, and / or power source may lead to different operations. In this example power generation is provided by a solar panel. Four areas are considered within each time period, the power generation and demand 110, the power available 11 1, the battery string demand 1 12 and the battery protection 113. This example aims to maximise the economic advantage of a residential energy storage system (comprising a battery system with a plurality of groups of at least one battery) paired with solar generation. This is achieved by storing excess solar power (solar power generated above the household's immediate demand) within the battery system (charging the energy storage system), and then subsequently discharging the battery system to power (or to supplement) the household at a later time in the day when demand for and / or the cost of purchasing electrical power from the grid is high. To this end, the idealised hierarchy for use of generated solar power is: 1 ) household base load ("excess" solar available only once the base load is covered), 2) charge energy storage system (storage of energy for later use), 3) sell to grid.

[0175] In the morning 100 the solar generation (which may be modelled as a normal distribution centred about midday) is beginning to provide powerto the household and begins to offset the baseload of the house (reduces the power necessary to purchase from the grid). As solar generation increases, the household's load is fully covered by solar energy, and further increases in power generation result in excess solar energy allowing for a recharge of the battery system to begin. Grid power may be available throughout this period, at low to moderate cost, but its use is to be avoided. In the morning, the BMS 10 will try to recharge thebattery string 17 as the LABs 20 are at a low SoC, such as 25%. To maximise battery protection at low SoC a high charge rate (power) is required to achieve sufficient (>150-200mV) positive electrode polarization. However, there is little availability of excess solar to provide this. Buying excess power from the grid, or other source reduces economic advantage to the user customer. Similarly deferring the battery charging reduces the opportunity to recharge the battery string 17 and potentially require the purchase of power from the grid.

[0176] In response the BMS 10 is configured to segregate and / or integrate independent LABs based on the charging power available. For example, the required charge polarisation may be achieved when battery charge current is greater than a charging threshold:[Battery Current] > [Minimum Battery Current]The charging threshold (minimum battery current) may be a predefined threshold, such as a minimum charge rate (e.g. 1 C as described above). Based on this the maximum number of LABs which can be charged from a given current source at any moment in time may be calculated as:[Maximum Number of Batteries] = Floor([Current Available] / [Minimum Battery Current])On average, excess solar current will increase toward noon, allowing an increasing number of LABs 20 to be brought into the battery system for charging.

[0177] In some cases, the charging is performed in discrete SoC blocks, such that, if one of the charging LABs 20 rises in SoC by some threshold or nominal value (for example 1 %, 2% or 5%, or 10% SoC), and there are other LABs with lower SoC, then the charging LAB 20 can be segregated from the battery system and another integrated in its place - in this manner, all LABs 20 can be ensured to receive at least some charge and the average SoC is spread across all the LABs 20 (or groups 17) of the battery system.

[0178] If the available excess power reduces at any point (for example because clouds reduces solar generation, or household demand increases), then the number of charging LABs in the battery system may be reduced (by segregating LABs 20) to ensure the maximum allowable number of LABs 20 are charged. Similarly, as the available power increases segregated LABs 20 can be activated and charging can continue for multiple LABs 20. In a situation where it is not possible to charge any LABs 20 because the available charging power is too low to charge even a single LAB 20 the BMS may export this unusably low power to the grid, although this will be dependent on the LABs state of health such as the LABs SoC.

[0179] At Midday 101 the solar panels are generally producing plenty of energy, allowing the LABs 20 to charge at high efficiency. This may be a period where balancing the SoC in the LABs 20 occurs, based on the potential different charging rates which were achieved earlier in the morning. This may also allow multiple LABs to charge at a determined charging threshold based on the battery system and the positive electrode overpotential requirements (e.g. 1 Q.

[0180] Figure 13 shows the battery management in the afternoon, evening and overnight portions of the day. In the Afternoon 102 the solar panel load is typically decreasing and the battery string 17 SoC is high after the day's charge. Charge polarisation of the LABs in the battery string 17 should be reduced at the high states of charge to avoid deleterious impacts of high potentials on the electrodes, and potential separator dryout. Charge polarization may be controlled by the BMS 10 at battery system 1 level, as it is set by the inverter 16 driving the battery system (although the BMS 10 controller 1 1 may control the inverter 16). In some cases, as LABs 20 reach the high SoC threshold they are segregated from the battery system 1, until all or a sufficient number of LABs 20 have reached this same high SoC threshold enabling the charge polarisation to be lowered.

[0181] In the evening 104 the LABs are being discharged to provide power to the household. The solar generation is low or stopped. Evening power demands are high, with some potentially very high peaks (e.g., where multiple appliances such as the stove, oven, heat pump, hot water jug operate concurrently). Advantageously, discharge current per LAB in the battery system 1 should be kept low, for example below a threshold maximum battery current. This can be achieved in the battery system 1 with independently controlled LABs (or groups of LABs) by integrating as many LABs to the battery system 1 as possible. This is easier where the afternoon 102 has been used to balance or equalize the SoC of all the LABs 20 (or groups of batteries) in the battery system 1 . This provides a maximum available discharge current, that is communicated to the charger or inverter 16, which is equal to the current of each LAB multiplied by the number of LABs 20 that are operational (e.g., 8). Additional current / power, if required, can be bought from the grid if there is insufficient battery power to satisfy the household requirements.

[0182] Where the LABs 20 do not have a substantially equal SoC the BMS 10 may discharge independent or groups of LABs 20 until the SoCs are substantially equalized. This is because LABs 20 of differing SoCs will have differing voltages. Higher SoC LABs 20 in parallelconnected groups will contribute higher currents (possibly exceeding current limits). Each additional LAB 20 able to be included in the system 1 will increase the maximum available discharge current. In some cases, the current in each LAB 20 will be different, due to internal resistance (for example, as a result of manufacturing tolerances and aging rate effects). This will mean that some LABs 20 will discharge faster than others. The SoC of each LAB 20 may be monitored during each discharge, with LABs 20 independently segregated / introduced into the battery system 1 depending on SoC and to maintain substantially equalized SoC. As LABs 20 reach their maximum allowed discharge (minimum SoC, for example 15%, 20%, 25%, 30%, 35% or 40%), LABs 20 are segregated from the battery system to prevent over discharge.

[0183] Overnight 105 the LABs 20 are ideally discharged to a low SoC during the overnight period through power use. This minimises the purchase of generally more expensive power from the grid. A low SoC may be less than 25%, less than 20%, or less than 15%, or said suitable low SoC can be determined based on the battery characteristics. However, if useful SoC is still present the LABs 20 may continue to discharge and / or run maintenance tasks such as a deep discharge (where power is present in the remaining LABs 20, or from the grid for recharging). Similarly, if an overcharge is required, grid purchased energy may be lower cost overnight, so grid power may be used without significantly reducing the overall system's economic advantage or operation. Advantageously the discharge rate may be set very low (low discharge rate is good for battery health). The discharge may only offset some of the household load, with the remaining household load being purchased from the grid.

[0184] As described the ability to independently charge LABs in a battery system (e.g. an energy storage system) allows a BMS to provide the required output power for an energy user, as well as applying one or more different methods for preserving the health, and increasing the lifetime of the LABs. It will be understood that further methods may also be used, and the various methods described may be used separately, or in conjunction with one another. In some cases, the methods are used in conjunction with a SoC balancing consideration, so that the SoC of each LAB is maintained at approximately the same level as the remaining batteries in the string and / or battery system to allow use of the full string without wasted energy moving between batteries.

[0185] In some cases, the BMS 10 may control a battery system comprising a plurality of groups of LABs. For example, the BMS 10 may control multiple parallel groups of LABs 17, with each LAB group 17 comprising one or more series-connected LABs 20. In such anarrangement, components would need to be specified for the higher battery group voltage. In some cases, multiple groups of parallel LABs could also be controlled. In some cases, the number of LABs 20 in a single parallel string is increased.

[0186] In some cases, the switching 18 and controller 11 components of the BMS 10 may be separated. For example, this may provide better scalability because multiple printed circuit boards could be used. In some cases, especially for larger installations, multiple switching boards may be used. For example, one switching board could be used for each LAB 20 with electronic communication back to a common controller 1 1. In some cases, this reduces the amount of cabling and / or circuit impedance and may increase system efficiency.

[0187] As used herein, the term "controller" refers broadly to any suitable device, logical block, module, circuit, or combination of elements for executing instructions. For example, the controller 1 1 can include any conventional general purpose single- or multi-chip microprocessor such as a Pentium™ processor, a MIPS™ processor, a Power PC™ processor, AMD™ processor, ARM™ processor, Microchip™ processor, or an ALPHA™ processor. In addition, the controller 1 1 can include any conventional special purpose microprocessor such as a digital signal processor or a microcontroller. The various illustrative logical blocks, modules, and circuits described in connection with the embodiments disclosed herein can be implemented or performed with a general purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein, or can be a pure software in the main processor. For example, aspects of the BMS 10 can be a software implemented function block within controller 1 1 which does not utilize any additional and / or specialized hardware elements. Controller 1 1 can be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a combination of a microcontroller and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration. In some cases, the BMS 10 and / or controller may be operated on a server in communication with the battery string 17, or at least receive updates and / or maintenance from a server and / or through a remote connection.

[0188] The memory, or data storage used to store the BMS and / or LAB data can refer to electronic circuitry that allows data to be stored and retrieved by the processor. Data storagecan refer to onboard devices or systems or external devices or systems, for example, disk drives or solid state drives. Data storage can also refer to fast semiconductor storage, for example, Random Access Memory (RAM) or various forms of Read Only Memory (ROM), which are directly connected to the controller 1 1. Data storage can be physical hardware configured to store data in a non-transitory medium.

[0189] Although certain embodiments and examples are disclosed herein, inventive subject matter extends beyond the specifically disclosed embodiments to other alternative embodiments and / or uses, and to modifications and equivalents thereof. Thus, the scope of the claims or embodiments appended hereto is not limited by any of the particular embodiments described herein. For example, in any method or process disclosed herein, the acts or operations of the method or process may be performed in any suitable sequence and are not necessarily limited to any particular disclosed sequence. Various operations may be described as multiple discrete operations in turn, in a manner that may be helpful in understanding certain embodiments; however, the order of description should not be construed to imply that these operations are order dependent. Additionally, some structures described herein may be embodied as integrated components or as separate components. For purposes of comparing various embodiments, certain aspects and advantages of these embodiments are described. Not necessarily all such aspects or advantages are achieved by any particular embodiment. Thus, for example, various embodiments may be carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other aspects or advantages as may also be taught or suggested herein.

[0190] It should be emphasized that many variations and modifications may be made to the embodiments described herein, the elements of which are to be understood as being among other acceptable examples. All such modifications and variations are intended to be included herein within the scope of this disclosure and protected by the following claims. Further, nothing in the foregoing disclosure is intended to imply that any particular component, characteristic or process step is necessary or essential.

Claims

CLAIMS1. A lead acid battery management system for charging a battery system comprising a plurality of groups of at least one lead acid battery each, the battery management system comprising: at least one control device configured to electrically integrate and segregate each of the groups of at least one battery from the battery system, and a controller configured to control the control device to independently control the charging and discharging of each of the groups of at least one battery wherein the controller is configured to: determine an input power available to charge the battery system, determine, based on the determined input power, that at least one of the groups of batteries can charge above a charging threshold; and selectively charge at least one of the groups of at least one battery.

2. The lead acid battery management system as claimed in claim 1 comprising the steps of: determining a number of the groups of at least one battery to be charged dependent on the determined input power; and selectively charging the determined number of groups of at least one battery.

3. The lead acid battery management system as claimed in claim 1 or 2 wherein the charging threshold is a cell charging potential threshold.

4. The lead acid battery management system as claimed in claim 1 or 2 wherein the charging threshold is a desired positive half-cell overpotential.

5. The lead acid battery management system as claimed in any one of claims 1 to 4 wherein the charging threshold is determined based on a desired positive half-cell overpotential.

6. The lead acid battery management system as claimed in claim 4 or claim 5 wherein the desired positive half-cell overpotential threshold is any one or more of: at least 10OmV, at least 150mV or at least 200mV.

7. The lead acid battery management system as claimed in claim 5 or claim 6 wherein the charging threshold is a threshold of an electrical characteristic of the lead acid batteries dependent on the positive half-cell overpotential.

8. The lead acid battery management system as claimed in any one of claims 4 to 7 wherein the selective charging of the at least one groups of at least one battery is controlled to achieve the desired positive half-cell overpotential.

9. The lead acid battery management system as claimed in any one of claims 1 to 8 wherein the controller is configured to: control a charge rate to maintain charging above the charging threshold.

10. The lead acid battery management system as claimed in claims 1 to 9 wherein the charging threshold is a minimum charging current.1 1 . The lead acid battery management system as claimed in claim 10 wherein the minimum charging current is based on the capacity of each of the plurality of groups of at least one battery.

12. The lead acid battery management system as claimed in claims 10 or 1 1 wherein the minimum charging current is predetermined.

13. The lead acid battery management system as claimed in claim 12 wherein the minimum charging current threshold comprises a charge rate, optionally wherein the charge rate is based on 5C capacity of the plurality of groups of at least one battery.

14. The lead acid battery management system as claimed in claims 12 or 13 wherein the minimum charging current threshold is between 0.7 and 1.4C, optionally at least 1 C.

15. The lead acid battery management system as claimed in any one of claims 1 to 14 wherein the charging threshold is applied below a threshold state of charge of each group of at least one battery.

16. The lead acid battery management system as claimed in claim 15 wherein the threshold state of charge is any one of 40%, 45%, 50%, 55% or 60%.

17. The lead acid battery management system as claimed in claim 1 to 16 comprising a charger, wherein determining the input power availability comprises determining a rated power of the charger.

18. The lead acid battery management system as claimed in claims 1 to 17 wherein determining the available input power comprises: receiving one or more measurements; and determining the available input power from the one or more measurements.

19. The lead battery management system as claimed in claims 1 to 18 wherein the groups of at least one battery are connected to the battery system in parallel.

20. The lead acid battery management system of as claimed in claims 1 to 19 wherein the controller is configured to monitor the state of charge of each of the groups of at least one battery, optionally with a coulomb counter.21 . The lead acid battery management system as claimed in claims 1 to 20 wherein the batteries comprise bipolar lead acid batteries.

22. The lead acid battery management system of claims 1 to 21 wherein the controller is configured to substantially balance the state of charge of each of the batteries in the battery string by rotating which of the groups of at least one battery are being charged.

23. The lead acid battery management system of claim 22 wherein the rotation is based on one or more of: a state of charge added to the group of at least one battery, a temperature of the group of at least one battery, and / or a time of charging of the group of at least one battery.

24. The lead acid battery management system of claims 1 to 21 wherein the controller is configured to determine a temperature of at least one group of the groups of at least one battery and adjust the charging threshold dependent on that temperature.

25. The lead acid battery management system of claims 1 to 24 wherein the controller is configured to rotate which of the groups of at least one battery are being charged, optionally wherein the controller is configured to modify the time between charging of each of the groups of at least one battery , or the number of groups of at least one battery being charged, based on a temperature of the groups or of at least one battery.

26. The lead acid battery management system of claims 1 to 25 wherein the battery management system is configured to receive power from a solar power source and / or a wind power source.

27. The lead acid battery management system of claims 1 to 26 wherein the controller is configured to:Selectively charge each of the groups of at least one battery to one of: a first target battery state of charge, and an overcharge above a full state of charge, the overcharge greater than the first target battery state of charge,Wherein the selection of the first target state of charge or overcharge is dependent on a charge characteristic of each battery.

28. The lead acid battery management system of claim 27 wherein the charge characteristic comprises any one or more of: a number of charges of each of the batteries to the first target battery state of charge, and / or a length of time since the last charge of each of the batteries to the over charge , and / or a state of charge of each of the batteries during discharge, and / or an electrical characteristic of each of the batteries.

29. The lead acid battery management system of claims 1 to 28 wherein the controller is configured to: receive a measurement of an electrical characteristic of each of the groups of at least one battery, determine a charge characteristic of at least one group of at least one battery from the electrical characteristic; and modify the discharging of the group of at least one battery based in the determined charge characteristic.

30. The lead acid battery management system of claim 29 wherein the charge characteristic comprises a state of charge.31 . The lead acid battery management system of claims 29 or 30 wherein the discharge is modified by any one or more of: preventing discharge of the at least one battery; decreasing a discharge rate; an over-discharge characteristic.

32. The lead acid battery management system as claimed in any one of claims 1 to 31 wherein the charging threshold is applied for a first portion of a charge.

33. A method of managing a plurality of lead acid batteries in a battery system, the battery system comprising a plurality of groups of at least one lead acid battery each, the method comprising the steps of: determining an input power available to charge the battery system, determining, based on the determined input power, that at least one of the groups of batteries can charge above a charging threshold; and selectively charging at least one of the groups of at least one battery.

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