System and method for parallel charging of battery packs

Abstract

Battery management system, comprising: a first set of batteries; a second set of batteries; a first charging circuit having a first switch for connecting the first battery pack to a power source to enable charging; a second charging circuit having a second switch for connecting the second battery pack to the power source to enable charging, the second charging circuit being arranged in parallel with the first charging circuit; and a processor programmed to: Receiving an input indicative of a first battery voltage and a second battery voltage; Closing the first switch and opening the second switch to enable charging of the first battery pack with a first charging current and to disable charging of the second battery pack when the first battery voltage is lower than the second battery voltage; and Closing the first and second switches to enable parallel charging of the first battery pack and the second battery pack when the first battery voltage is approximately equal to the second battery voltage.

Description

TECHNICAL FIELD

[0001] One or more embodiments relate to a battery management system for charging a battery assembly comprising multiple battery packs. BACKGROUND

[0002] Electrified vehicles, including pure electric vehicles and hybrid electric vehicles, include a high-voltage battery pack used for propulsion or "traction" of the vehicle, which may be referred to as a traction battery. Such electrified vehicles include power electronics for converting the energy supplied by the traction battery, which is rated for a maximum voltage of approximately 400 volts.

[0003] US2019 / 0359067A1 discloses methods for a reconfigurable battery charging controller. US2014 / 0312828A1 discloses a method and apparatus for generating a dynamically reconfigurable energy storage device. EP3566894A1 discloses a battery pack for vehicles. US2019 / 0256018A1 describes a power supply system for vehicles, and US2018 / 0105060A1 describes a system and apparatus for charging a vehicle battery.

[0004] The object of the present invention is to provide a particularly efficient battery management system, in particular for use in vehicles.

[0005] This object is achieved by a battery management system according to one of claims 1 or 12 or by a method for charging a battery arrangement according to claim 15. Advantageous further developments are specified in the dependent claims. SUMMARY

[0006] In one embodiment, a battery management system is provided with a first battery pack and a second battery pack. A first charging circuit includes a first switch for connecting the first battery pack to a power source to enable charging. A second charging circuit includes a second switch for connecting the second battery pack to the power source to enable charging, wherein the second charging circuit is arranged in parallel with the first charging circuit.A processor is programmed to: receive an input indicative of a first battery voltage and a second battery voltage; close the first switch and open the second switch to enable charging of the first battery pack at a first charging current and disable charging of the second battery pack in response to the first battery voltage being less than the second battery voltage; and close the first switch and close the second switch to enable parallel charging of the first battery pack and the second battery pack in response to the first voltage being approximately equal to the second battery voltage.

[0007] Implementations may include one or more of the following features. For example, the first battery pack and the second battery pack may be adapted to provide direct current with a maximum voltage of approximately 400 volts. The battery management system may include a discharge circuit with a discharge switch for connecting the first battery pack and the second battery pack in series to jointly provide direct current with a maximum voltage of approximately 800 volts.

[0008] As another example, the battery management system may include a precharge switch and a series-connected resistor, wherein the precharge switch, along with the resistor, is connected in parallel with the first switch. The processor may be further programmed to: close the precharge switch and open the first switch to enable precharging of the first battery pack; and, in response to a precharge voltage exceeding a precharge threshold, open the precharge switch and close the first switch to enable charging of the first battery pack.

[0009] Furthermore, the processor may be further programmed to reduce the first charging current to a second charging current when the first charging current exceeds a charging current threshold and / or the difference between the first battery voltage and the second battery voltage is less than a predetermined threshold. Furthermore, the second charging current may be approximately half of the first charging current. Furthermore, the processor may be programmed to reduce the second charging current to a third charging current when the difference between the first battery voltage and the second battery voltage is less than the predetermined threshold, wherein the third charging current is approximately half of the second charging current.

[0010] As another example, the processor may be further programmed to close the second switch and open the first switch to enable charging of the second battery pack with a second battery pack charging current in response to an input indicating that the second battery voltage is less than the first battery voltage. The battery management system may include a pre-charge switch and a resistor connected in series, the pre-charge switch, along with the resistor, connected in parallel with the second switch, the processor further programmed to: close the pre-charge switch and open the second switch to enable pre-charging of the second battery pack; and in response to a pre-charge voltage exceeding a pre-charge threshold, open the pre-charge switch and close the second switch to enable charging of the second battery pack.Furthermore, the processor may be programmed to reduce the charging current of the second battery pack in response to a difference between the second battery voltage and the first battery voltage being less than a predetermined threshold.

[0011] In another embodiment, a battery management system is provided with a first charging circuit comprising a first switch for connecting a first battery pack to a power source. A second charging circuit comprises a second switch for connecting a second battery pack to the power source, the second charging circuit being arranged in parallel with the first charging circuit. A discharging circuit comprises a discharging switch for connecting the first battery pack and the second battery pack in series.A processor is programmed to: open the discharge switch; receive an input indicative of a first battery voltage and a second battery voltage; close the first switch and open the second switch in response to the first battery voltage being less than the second battery voltage; and close the first switch and close the second switch in response to the first battery voltage being approximately equal to the second battery voltage.

[0012] Implementations may include one or more of the following features. For example, the battery management system may include a precharge switch and a resistor connected in series, the precharge switch, along with the resistor, connected in parallel with the first switch, the processor further programmed to: close the precharge switch and open the first switch to enable precharging of the first battery pack; and in response to a precharge voltage exceeding a precharge threshold, open the precharge switch and close the first switch to enable charging of the first battery pack. Further, the processor may be programmed to reduce a first charging current to a second charging current when the difference between the first battery voltage and the second battery voltage is less than a predetermined threshold.

[0013] In another embodiment, a method for charging a battery assembly is provided. A discharge switch connected between a first battery pack and a second battery pack is opened. An input indicative of a first battery voltage and a second battery voltage is received. A first switch connecting the first battery pack to a power source is closed to enable charging of the first battery pack with a first charging current when the first battery voltage is lower than the second battery voltage. The first switch and a second switch are closed to connect the second battery pack to the power source to enable parallel charging of the first battery pack and the second battery pack when the first battery voltage is approximately equal to the second battery voltage.

[0014] Implementations may include one or more of the following features. For example, a precharge switch and a resistor may be connected in series, with the precharge switch, along with the resistor, connected in parallel with the first switch. The precharge switch is closed and the first switch is open to enable precharging of the first battery pack. The precharge switch is opened and the first switch is closed to enable charging of the first battery pack when a precharge voltage exceeding the precharge threshold occurs.

[0015] The first charging current may be reduced to a second charging current if the difference between the first battery voltage and the second battery voltage is less than a predetermined threshold.

[0016] As another example, in response to an input indicating that the second battery voltage is less than the first battery voltage, the second switch may be closed and the first switch may be opened to enable charging of the second battery pack at a second charging current.

[0017] As another example, a precharge switch and a resistor may be connected in series, with the precharge switch, along with the resistor, connected in parallel with the second switch. The precharge switch is closed and the second switch is open to enable precharging of the second battery pack. The precharge switch is opened and the second switch is closed to enable charging of the second battery pack when the precharge thresholds are exceeded. The second charging current may be reduced to a third charging current when the difference between the second battery voltage and the first battery voltage is less than a predetermined threshold. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic diagram of a battery management system including an HV power distribution module, a first battery pack, and a second battery pack according to one or more embodiments. Fig. 2 is a circuit diagram showing a battery connection unit of the HV power distribution module of Fig. 1 shows. Fig. 3 is a circuit diagram showing the battery connection unit of Fig. 2 in a discharge configuration with both battery sets connected in series. Fig. 4 is a circuit diagram showing the battery connection unit of Fig. 2 in a first battery charging configuration for charging the first battery pack. Fig. 5 is a circuit diagram showing the battery connection unit of Fig. 2 in a second battery charging configuration for charging the second battery pack. Fig. 6 is a circuit diagram showing the battery connection unit of Fig. 2 in a parallel charging configuration where both battery sets are connected in parallel. Fig. 7 is a flowchart illustrating a method for charging the battery assembly of Fig. 1 illustrates. DETAILED DESCRIPTION

[0018] As required, detailed embodiments of the present invention are disclosed herein; however, it should be understood that the disclosed embodiments are merely exemplary of the invention that may be embodied in various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or reduced to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for showing one skilled in the art how to variously employ the present invention.

[0019] With reference to Fig. 1, a battery management system according to one or more embodiments is illustrated and generally designated by the numeral 100. The battery management system 100 is included in a vehicle (not shown) and includes a high-voltage (HV) power distribution module 104. The HV power distribution module 104 electrically connects an external power source 106 to a traction battery assembly 108 to facilitate charging. The HV power distribution module 104 also connects to vehicle loads 105, such as traction motors, heaters, etc., to discharge the traction battery assembly 108.

[0020] The external power source 106 is electrically connected to the electric vehicle supply equipment (EVSE) 110, such as a charger or charging station. The external power source 106 is an electrical power distribution network, such as that provided by a power utility, according to one or more embodiments. The EVSE 110 includes circuitry and controls to regulate and control the transfer of power between the external power source 106 and the battery management system 100. The external power source 106 provides alternating current (AC) to the EVSE 110, which is converted to direct current (DC). Typical electrified vehicles include a traction battery with a maximum voltage of approximately 400 volts; accordingly, the EVSE 110 is designed to provide charging for a 400-volt HV battery.

[0021] The traction battery assembly 108 includes two battery packs, a first battery pack 112 and a second battery pack 114, connected in series to provide the battery assembly with an output voltage greater than the voltage of each individual battery pack. In one embodiment, each battery pack 112, 114 provides a maximum voltage of approximately 400 volts, and the battery assembly 108 provides a maximum voltage of approximately 800 volts. The HV power distribution module 104 also includes a battery interconnect unit 116 that connects the traction battery assembly 108 to the EVSE 110 in various configurations, such as series and parallel, to facilitate charging the traction battery assembly 108 at a lower voltage, such as charging an 800-volt traction battery assembly 108 with a 400-volt EVSE 110.The battery management system 100 also includes a controller 118, comprising a processor 120 and a memory 122, for controlling the battery interconnect unit 116. The controller 118 conditions the power supplied by the external power source 106 to provide the proper voltage and current levels to the traction battery assembly 108 to facilitate charging.

[0022] Referring to Fig. 2, the battery connection unit 116 comprises a plurality of switches (S A -S G ) that are controlled to open and close to provide numerous battery charging and discharging circuits or configurations. In one or more embodiments, each switch (S A -S G ) a relay designed to withstand the high voltages and currents present in the circuits. The controller 118 provides the battery connection unit 116, as shown in Fig. 1, a control signal (CONTROL) is available to control each switch (S A -S G ) individually. The controller 118 receives input signals that represent the accumulated voltage (V A ) of the first battery set 112 and the accumulated voltage (V B ) of the second battery pack 114, as shown in Fig. 1. The controller 118 may receive such voltage signals directly from battery sensors or from one or more other vehicle control units via a vehicle bus.

[0023] With reference to Fig. 3, the battery connection unit 116 provides a discharge circuit 124 to supply power from the first battery pack 112 and the second battery pack 114 to the vehicle loads 105 (shown in Fig. 1). The discharge circuit 124 comprises: a switch S G , which is connected in the path to the second battery set 114, a switch S A, which is connected in series between the second battery set 114 and the first battery set 112, and a switch S B , which is connected in a discharge path downstream of the first battery set 112. The discharge current (I d ) through the discharge circuit 124 is in Fig. 3 represented by a dashed line.

[0024] In one or more embodiments, the controller 118 controls the switch S C , switch S G and switch S A , so that they are closed to enable precharging of the first battery pack 112 and the second battery pack 114 until a precharge voltage exceeds a precharge threshold. The precharge voltage is an indicator of a capacitive load voltage and is measured at point 135 according to one or more embodiments. Next, the controller 118 controls the switch S C to open and switch S Bto close. The controller 118 then begins discharging the first battery set 112 and the second battery set 114.

[0025] According to Fig. 4, the battery connection unit 116 includes a first charging circuit 126 for charging the first battery pack 112. The first charging circuit 126 connects the first battery pack 112 to the external power source 106 and the EVSE 110 (shown in Fig. 1) to receive power. The first charging circuit 126 includes a primary charging path 128 and a return path 130. The primary charging path 128 extends to the first battery pack 112 and includes the switch S B . The return path 130 extends from the first battery pack 112 and includes the switch S D . The first charging circuit 126 also includes a pre-charging path 132 that connects the switch S C and a first resistor 134, which are connected in series. The switch S Cis connected together with the first resistor 134 in parallel to the switch S B The first resistor 134 has a value of approximately 30-50 ohms according to one or more embodiments. The precharge path 132 is used to avoid a large inrush current when the first battery pack 112 is connected directly to a capacitive load, such as a traction motor.

[0026] The controller 118 controls the switch S B , switch S C and switch S D such that they are individually opened and closed to enable and disable charging of the first battery pack 112. In one or more embodiments, the controller 118 controls the switch S C and switch S Dto close to enable precharging of the first battery pack 112 until a precharge voltage exceeds a precharge threshold. The precharge voltage is an indicator of a capacitive load voltage and is measured at point 135 according to one or more embodiments. Next, the controller 118 controls the switch S C to open and switch S B to close. Then, the controller 118 begins charging the first battery pack 112 with a first charging current (I c1 ), which in Fig. 4 is shown by a dashed line.

[0027] With reference to Fig. 5, the battery connection unit 116 includes a second charging circuit 136 for charging the second battery pack 114. The second charging circuit 136 connects the second battery pack 114 to the external power source 106 and the EVSE 110 (shown in Fig. 1) to receive power. The second charging circuit 136 includes a primary charging path 138 and a return path 140. The primary charging path 138 extends to the second battery pack 114 and includes a switch S E . The return path 140 leads away from the second battery set 114 and includes the switch S G . The second charging circuit 136 also includes a pre-charging path 142 which includes a switch S F and a second resistor 144, which are connected in series. The switch S F is connected together with the second resistor 144 in parallel to the switch S E The precharge path 142 is used to avoid a large inrush current when the second battery pack 114 is connected directly to a capacitive load.

[0028] The controller 118 controls the switch S E , switch S F and switch S Gsuch that they are individually opened and closed to enable and disable charging of the second battery pack 114. In one or more embodiments, the controller 118 controls the switch S F and switch S G to close to enable precharging of the second battery pack 114 until a precharge voltage exceeds a precharge threshold. The precharge voltage is an indicator of a capacitive load voltage and is measured at point 135 according to one or more embodiments. Next, the controller 118 controls the switch S F to open and switch S E to close. Then, the controller 118 begins charging the second battery pack 114 with a second charging current (I c2 ), which in Fig. 5 is shown by a dashed line.

[0029] According to Fig. 6, the battery connection unit 116 can be controlled to charge the first battery pack 112 and the second battery pack 114 in parallel. The controller 118 controls the switch S B and switch S D so that they are closed to enable charging of the first battery pack 112 with the first charging current (I c1 ) as described above with reference to Fig. 4. The controller 118 also controls the switch S E and switch S G so that they close to enable charging of the second battery pack 114 with the second charging current (I c2 ) as described above with reference to Fig. 5 described.

[0030] With reference to Fig. 7, a method for charging a battery assembly is illustrated and generally designated by the numeral 200 in accordance with one or more embodiments. The method 200 is implemented using software code included in the controller 118, according to one or more embodiments. While the method is described using flowcharts illustrated as a series of sequential steps, in one or more other embodiments, one or more steps may be omitted and / or performed in a different manner. In other embodiments, the software code is distributed across multiple controllers, such as the controller 118 and one or more vehicle controllers (not shown).

[0031] Although the controller 118 is illustrated as a single controller, it may include multiple controllers or be embodied as software code within one or more other controllers. The controller 118 generally includes any number of microprocessors, ASICs, ICs, memory (e.g., FLASH, ROM, RAM, EPROM, and / or EEPROM), and software code that cooperate with one another to perform a series of operations. This hardware and / or software may be grouped together in arrays to perform specific functions. One or more of the controllers or devices described herein include computer-executable instructions that may be compiled from or interpreted from computer programs created using a variety of programming languages ​​and / or technologies.Generally, a processor (e.g., a microprocessor) receives instructions, for example, from memory, a computer-readable medium, or the like, and executes the instructions. A processing unit includes a non-transferable, computer-readable storage medium capable of executing instructions of a software program. The computer-readable storage medium may be, but is not limited to, an electronic storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any combination thereof. The controller 118 also includes predetermined data or "lookup tables" stored in the memory according to one or more embodiments.

[0032] In step 202, the controller 118 receives an input indicating that the voltage of one battery pack is greater than that of the other battery pack. The controller 118 then begins charging the battery pack with the lower voltage. Fig. 7, the first battery pack 112 has a lower voltage than the second battery pack 114, ie V A < V B , and the controller 118 controls the switches of the battery connection unit 116 to enable the first charging circuit 126, as described with reference to Fig. 4 described.

[0033] In step 204, the controller 118 sets the requested charging voltage (Vreq). The controller 118 may set the requested charging voltage (Vreq) based on the sum of the voltages of the other battery pack, ie, V B, and a predetermined value (C) to take into account inefficiencies such as line losses, connector losses, etc. (Vreq = V B + C). In one or more embodiments, C is equal to a value between 4 and 5 volts. In step 206, the controller 118 sets the requested charging current (Ireq) to a first predetermined current value (I1).

[0034] In step 208, the controller compares 118 V A with V B . The controller 118 compares the absolute value of the difference between V A and V B with a given threshold value (K1) to determine whether the difference is less than or equal to K1 (|V A -V B | ≤ K1). If the determination in step 208 is negative, the controller 118 returns to step 206 to continue charging the first battery pack 112 with I1. If the determination in step 208 is positive, the controller 118 proceeds to step 210.

[0035] In step 210, the controller 118 compares the measured charging current I1 with a charging current threshold (Ia) to determine whether I1 is less than or equal to Ia. In one or more embodiments, Ia is equal to a current value between 10A and 15A. If the determination in step 210 is positive, i.e., (I1 ≤ Ia), the controller 118 proceeds to step 212 and terminates the charging process of the first battery pack 112 by setting Ireq to zero.

[0036] In step 214, the controller 118 controls the switches of the battery connection unit 116 to enable parallel charging of the first battery pack 112 and the second battery pack 114, as described with reference to Fig.6. In step 216, the controller 118 controls the parallel charging of the first battery pack 112 and the second battery pack 114 until the first battery pack 112 or the second battery pack 114 reaches a charging limit, such as a state of charge limit or a voltage limit, such as 400 volts. Then, the controller 118 stops the charging process of the battery packs 112, 114.

[0037] If the determination in step 210 is negative, ie, I1 is greater than Ia, the controller 118 proceeds to step 218 to reduce the charging current. If I1 is greater than Ia, this indicates that the accumulated voltage of the first battery set (V A) may be greater than the actual voltage of the first battery pack 112 because a high current through the resistance, such as the wire resistance, results in a high voltage drop, and therefore the determination in step 208 may not have been correct. In step 218, the controller 118 sets the requested charging current (Ireq) to a second predetermined current value (I2) that is less than I1. In one or more embodiments, I2 is a value approximately half of I1.

[0038] In step 220, the controller compares 118 V A with V B . The controller 118 compares the absolute value of the difference between V A and V B with a given threshold value (K2) to determine whether the difference is less than or equal to K2 (|V A -V B| ≤ K2). According to one or more embodiments, K2 may be equal to K1. If the determination in step 220 is negative, the controller 118 returns to step 218 to continue charging the first battery pack 112 with I2. If the determination in step 220 is positive, the controller 118 proceeds to step 222.

[0039] In step 222, the controller 118 compares the charging current I2 with the charging current threshold (Ia) to determine whether I2 is less than or equal to Ia. If I2 is less than or equal to Ia, the controller 118 proceeds to step 212 and terminates the charging process of the first battery pack 112. If not, i.e., if I2 is greater than Ia, the controller proceeds to step 224 to further reduce the charging current.

[0040] In step 224, the controller 118 sets the requested charging current (Ireq) to a third predetermined current value (In) that is less than I2. In one or more embodiments, In is a value approximately half of I2.

[0041] In step 226, the controller compares 118 V A with V B to determine whether the absolute value of the difference between V A and V Bis less than or equal to K3. K3 may be equal to K1 according to one or more embodiments. If the determination in step 226 is negative, the controller 118 returns to step 224 to continue charging the first battery pack 112 with I3. If the determination in step 226 is positive, the controller 118 proceeds to step 228 to determine if In is less than or equal to Ia. If so, the controller 118 proceeds to step 212 and stops charging the first battery pack 112. The method 200 may include several additional steps, such as steps 224-228, to further reduce the charging current until the charging current is less than Ia.

[0042] The method 200 shows an example in which the first battery pack 112 has a lower voltage than the second battery pack 114, ie, V A < V BHowever, the method 200 may be modified to accommodate a scenario where the second battery pack 114 has a lower voltage than the first battery pack 112.

[0043] While exemplary embodiments are described above, these embodiments are not intended to describe all possible forms of the invention. Rather, the words used in the description are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention. Furthermore, the features of the various embodiments may be combined to form further embodiments of the invention.

Claims

[1] Battery management system comprising: a first set of batteries; a second set of batteries; a first charging circuit having a first switch for connecting the first battery pack to a power source to enable charging; a second charging circuit having a second switch for connecting the second battery pack to the power source to enable charging, the second charging circuit being arranged in parallel with the first charging circuit; and a processor programmed to: Receiving an input indicative of a first battery voltage and a second battery voltage; Closing the first switch and opening the second switch to enable charging of the first battery pack with a first charging current and to disable charging of the second battery pack when the first battery voltage is lower than the second battery voltage; and Closing the first and second switches to enable parallel charging of the first battery pack and the second battery pack when the first battery voltage is approximately equal to the second battery voltage. [2] The battery management system of claim 1, wherein the first battery pack and the second battery pack are each adapted to provide direct current having a maximum voltage of about 400 volts. [3] The battery management system of claim 1, further comprising a discharge circuit having a discharge switch for connecting the first battery pack and the second battery pack in series to jointly provide direct current having a maximum voltage of about 800 volts. [4] The battery management system of claim 1, further comprising a pre-charge switch and a series-connected resistor, the pre-charge switch along with the resistor being connected in parallel with the first switch, the processor further being programmed to: Closing the pre-charge switch and opening the first switch to enable pre-charging of the first battery pack; and in response to a pre-charge voltage exceeding a pre-charge threshold, opening the pre-charge switch and closing the first switch to enable charging of the first battery pack. [5] The battery management system of claim 1, wherein the processor is further programmed to reduce the first charging current to a second charging current when the difference between the first battery voltage and the second battery voltage is less than a predetermined threshold and the first charging current exceeds a charging current threshold. [6] The battery management system of claim 1, wherein the processor is further programmed to reduce the first charging current to a second charging current in response to a difference between the first battery voltage and the second battery voltage being less than a predetermined threshold. [7] The battery management system of claim 6, wherein the second charging current is approximately equal to half of the first charging current. [8] The battery management system of claim 6, wherein the processor is further programmed to reduce the second charging current to a third charging current when the difference between the first battery voltage and the second battery voltage is less than the predetermined threshold, the third charging current being approximately equal to half of the second charging current. [9] The battery management system of claim 1, wherein the processor is further programmed to close the second switch and open the first switch to enable charging of the second battery pack at a second battery pack charging current in response to an input indicating that the second battery voltage is less than the first battery voltage. [10] The battery management system of claim 9, further comprising a pre-charge switch and a resistor connected in series, the pre-charge switch together with the resistor being connected in parallel with the second switch, the processor further being programmed to: Closing the pre-charge switch and opening the second switch to enable pre-charging of the second battery pack; and in response to a pre-charge voltage exceeding a pre-charge threshold, opening the pre-charge switch and closing the second switch to enable charging of the second battery pack. [11] The battery management system of claim 9, wherein the processor is further programmed to reduce the charging current of the second battery pack in response to a difference between the second battery voltage and the first battery voltage being less than a predetermined threshold. [12] Battery management system comprising: a first charging circuit having a first switch for connecting a first set of batteries to a power source; a second charging circuit having a second switch for connecting a second battery pack to the power source, the second charging circuit being arranged in parallel with the first charging circuit; a discharge circuit having a discharge switch for connecting and disconnecting the first battery pack and the second battery pack in series; and a processor programmed to: Opening the discharge switch; receiving an input indicating a first battery voltage and a second battery voltage; Closing the first switch and opening the second switch in response to the first battery voltage being less than the second battery voltage; and Closing the first switch and closing the second switch in response to the first battery voltage being approximately equal to the second battery voltage. [13] The battery management system of claim 12, further comprising a pre-charge switch and a series-connected resistor, the pre-charge switch together with the resistor being connected in parallel with the first switch, the processor being further programmed to: Closing the pre-charge switch and opening the first switch to enable pre-charging of the first battery pack; and in response to a pre-charge voltage exceeding a pre-charge threshold, open the pre-charge switch and close the first switch to enable charging of the first battery pack. [14] The battery management system of claim 12, wherein the processor is further programmed to reduce a first charging current to a second charging current when the difference between the first battery voltage and the second battery voltage is less than a predetermined threshold. [15] A method of charging a battery assembly, comprising: Opening a discharge switch connected between a first set of batteries and a second set of batteries; Receiving an input indicative of a first battery voltage and a second battery voltage; Closing a first switch to connect the first battery pack to a power source to enable charging of the first battery pack with a first charging current when the first battery voltage is lower than the second battery voltage; and Closing the first switch and closing a second switch to connect the second battery pack to the power source to enable parallel charging of the first battery pack and the second battery pack when the first battery voltage is approximately equal to the second battery voltage. [16] The method of claim 15, further comprising: Providing a pre-charge switch and a series-connected resistor, wherein the pre-charge switch together with the resistor is connected in parallel to the first switch; Closing the pre-charge switch and opening the first switch to enable pre-charging of the first battery pack; and in response to a pre-charge voltage exceeding a pre-charge threshold, opening the pre-charge switch and closing the first switch to enable charging of the first battery pack. [17] The method of claim 15, further comprising reducing the first charging current to a second charging current in response to a difference between the first battery voltage and the second battery voltage being less than a predetermined threshold. [18] The method of claim 15, further comprising closing the second switch and opening the first switch to enable charging of the second battery pack with a second charging current in response to an input indicating that the second battery voltage is less than the first battery voltage. [19] The method of claim 18, further comprising reducing the second charging current to a third charging current in response to a difference between the second battery voltage and the first battery voltage being less than a predetermined threshold. [20] The method of claim 15, further comprising: Providing a pre-charge switch and a series-connected resistor, wherein the pre-charge switch together with the resistor is connected in parallel to the second switch; Closing the pre-charge switch and opening the second switch to enable pre-charging of the second battery pack; and in response to a pre-charge voltage exceeding a pre-charge voltage threshold, opening the pre-charge switch and closing the second switch to enable charging of the second battery pack.

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