Combined battery pack, battery connection method therefor, and heterogeneous battery mixed type combined battery pack

Abstract

The present invention provides a long-life combined battery pack that takes into consideration measures against sparks when the switches are opened and closed. The combined battery pack 10 includes multiple battery packs 12, an integrated battery management system 14, and a lead-acid battery pack 16. Each of the multiple battery packs 12 contains multiple lithium-ion batteries 12a and further includes a contactor switch 12c. The lead-acid battery pack 16 is connected in parallel to the multiple battery packs 12. The integrated battery management system 14 controls the contactor switch 12c of the first battery pack to open when the voltage of the first battery pack deviates from a predetermined operating voltage range, and controls the contactor switch 12c of the second battery pack to close when the relationship between the voltage difference ΔV between the second battery pack and the lead-acid battery pack 16, the maximum current Imax that the second battery pack can pass, and the internal resistance R of the second battery pack satisfies equation (1).

Description

[Technical Field]

[0001] The present invention relates to a combined battery pack composed of a plurality of lead-acid batteries and a plurality of lithium-ion batteries connected in parallel with each other, a battery connection method therefor, and a heterogeneous battery mixed combined battery pack. [Background technology]

[0002] It has been known that a combined battery in which a lead-acid battery and a lithium-ion battery are connected in parallel can increase the stored energy per unit weight and improve the low-temperature power performance in particular. Various techniques have been disclosed to improve the safety of combined batteries.

[0003] Meanwhile, with regard to safety when the secondary batteries that make up the energy storage device deteriorate, Patent Document 1 discloses a charge / discharge control device that measures the current value of each cell during charging and controls a switching element to disconnect any abnormal cells detected based on this measurement from the parallel connection. Patent Document 2 also describes a railway vehicle battery system that includes one or more battery boxes containing multiple parallel-connected battery groups, and minimizes the number of contactors required to suppress cross current between battery groups or battery boxes. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2013-038884 [Patent Document 2] Patent Publication No. 2023-175463 Summary of the Invention [Problem to be solved by the invention]

[0005] However, Patent Document 1 has the problem of not taking into consideration measures against sparks when the switch is opened and closed. Patent Document 2 also has the problem of complex processing, in that in order to determine whether the contactor can be closed, the closed-circuit voltage when a cross current occurs must be calculated using the open-circuit voltage of the cell, and the criteria for determining whether the contactor can be closed must be changed depending on whether the cross current is a charging current or a discharging current. Furthermore, because Patent Document 2 does not take into consideration the possibility of not only charging but also discharging when charging is possible, there is the problem that it is not possible to align the voltages of the storage battery group or battery box and connect them to each other in a short period of time while charging is possible.

[0006] The present invention has been made in consideration of the above-mentioned problems of the prior art, and an object of the present invention is to provide a long-life combined battery pack that takes into consideration measures against sparks when opening and closing switches, a battery connection method therefor, and a combined battery pack that mixes different types of batteries. In addition to the above-mentioned objects, another object of the present invention is to provide a combined battery pack that requires simple processing and can be interconnected in a short time, a battery connection method therefor, and a combined battery pack that mixes different types of batteries. [Means for solving the problem]

[0007] In order to achieve the above object, the inventors have conducted extensive research and have discovered that by first preventing an overcurrent from flowing when the switch is turned on, it is possible to prevent sparks from occurring or to minimize damage to the switch even if a spark occurs.

[0008] The inventors also discovered that by charging and discharging the combined battery pack and bringing the voltage on the combined battery pack side closer to the voltage of the unconnected batteries, it is possible to prevent an overcurrent from flowing when the battery is switched on, and this discovery led to the present invention.

[0009] That is, a first embodiment of the present invention is a combined battery pack including a plurality of battery packs, each of which incorporates a plurality of lithium-ion batteries and further includes a battery management system and a contactor switch, an integrated battery management system, and a lead-acid battery pack connected in parallel to the plurality of battery packs, wherein the integrated battery management system controls opening and closing of the contactor switch based on battery information including voltage, current, and temperature collected from the battery management system of each battery pack, and the integrated battery management system determines in advance that the voltage of a first battery pack among the plurality of battery packs is low when charging or discharging the combined battery pack. Same for multiple battery packs The present invention provides a combined battery pack that controls the contactor switch of a first battery pack to open when the voltage deviates from a specified operating voltage range, and controls the contactor switch of a second battery pack to close when the relationship between the voltage difference ΔV between a second battery pack and a lead-acid battery pack among a plurality of battery packs, the maximum current Imax that the second battery pack can pass, and the internal resistance R of the second battery pack satisfies the following formula (1). 0 ≤ |ΔV| <Imax×R···(1)

[0010] In addition, in a second embodiment of the present invention, in order to configure a combined battery pack as a preliminary step, a plurality of lithium ion batteries are arranged inside a housing, and the lithium ion batteries are connected in parallel to form parallel groups, and a lead acid battery pack configured by connecting a pre-calculated number of lead acid batteries in series to each parallel group of lithium ion batteries is connected in parallel to each parallel group of lithium ion batteries, and a data line for measuring the voltage Va of each lithium ion battery is connected between the integrated battery management system and each lithium ion battery, and a data line for measuring the voltage Vb of the lead acid battery pack is connected between the integrated battery management system and the lead acid battery pack, and the integrated battery management system acquires the internal impedance R' and maximum allowable current I'max of each lithium ion battery in advance, and measures the internal impedance R' and maximum allowable current I'max of each lithium ion battery, and measures the internal impedance V' and maximum allowable current I'max of each lithium ion battery connected in series to each lithium ion battery. and confirming that the contactor switch is open, and after completing preliminary preparations, the integrated battery management system performs a voltage raising and lowering operation in which the integrated battery management system charges the combined battery pack until the voltage value reaches a preset first range, and then discharges the combined battery pack until the voltage value reaches a preset second range, and repeats this process; and during the voltage raising and lowering operation, when the voltage difference ΔV' between the voltage Va of one of the lithium-ion batteries and the voltage Vb of the lead-acid battery pack satisfies the following formula (2), the integrated battery management system performs a battery connecting operation to close the contactor switch connected in series to one of the lithium-ion batteries, and repeats the battery connecting operation for another of the lithium-ion batteries. 0≦|ΔV´| <I´max×R´···(2)

[0011] Here, in the above, the lead-acid battery pack is a plurality of lead-acid battery packs connected in parallel with each other, and if the voltage difference between the lead-acid battery packs increases while the integrated battery management system repeatedly charges and discharges the combined battery pack, it is preferable that the integrated battery management system fully charges the combined battery pack and then leaves it for 10 to 30 hours to equalize the voltages of the lead-acid battery packs.

[0012] Furthermore, a third embodiment of the present invention provides a heterogeneous battery mixed combined battery pack configured by connecting a plurality of battery packs and a lead-acid battery pack having different operating voltage ranges in parallel, wherein each of the plurality of battery packs includes a plurality of lithium-ion batteries connected in series and parallel to each other, and a contactor switch connected in series to the plurality of lithium-ion batteries, wherein each contactor switch is controlled to close when the voltage of the heterogeneous battery mixed combined battery pack is within the operating voltage range of each battery pack, and is controlled to open when the voltage is outside the operating voltage range, and the lead-acid battery pack operates within a voltage range from the maximum operating voltage to the minimum operating voltage of the heterogeneous battery mixed combined battery pack. [Effects of the Invention]

[0013] According to the present invention, measures against sparks when the switch is opened and closed are taken into consideration, so that the switch can have a long life. Furthermore, in addition to the above effects, the present invention has simple processing contents and allows interconnection in a short time. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a block diagram showing a combined battery pack according to a first embodiment of the present invention; [Figure 2] FIG. 10 is a block diagram showing a heterogeneous battery mixed combined battery pack according to a third embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0015] The combined battery pack, the battery connection method thereof, and the heterogeneous battery mixed type combined battery pack of the present invention will be described in detail below with reference to preferred embodiments shown in the accompanying drawings. First, the combined battery pack of the first embodiment of the present invention will be described in detail. Figure 1 is a block diagram showing the combined battery pack of the first embodiment of the present invention.

[0016] The combined battery pack 10 of the first embodiment of the present invention includes a plurality of battery packs 12, an integrated battery management system 14, and a lead-acid battery pack 16. Each of the plurality of battery packs 12 contains a plurality of lithium-ion batteries 12a and further includes a battery management system 12b and a contactor switch 12c. The lead-acid battery pack 16 is connected in parallel with the plurality of battery packs 12 to prevent sparks from occurring when the integrated battery management system 14 opens the contactor switch 12c.

[0017] The integrated battery management system 14 controls the opening and closing of the contactor switch 12c based on battery information including voltage, current, and temperature collected from the battery management system 12b of each battery pack 12. Furthermore, when charging or discharging the combined battery pack 10, the integrated battery management system 14 controls the contactor switch 12c of the first battery pack to open if the voltage of the first battery pack among the multiple battery packs 12 deviates from a predetermined operating voltage range. Furthermore, in order to reduce the inrush current when the contactor switch 12c is closed, the integrated battery management system 14 controls the contactor switch 12c of the second battery pack to close when the relationship between the voltage difference ΔV between a second battery pack among the multiple battery packs 12 and the lead-acid battery pack 16, the maximum current Imax that the second battery pack can pass, and the internal resistance R of the second battery pack satisfies the following formula (1): 0 ≤ |ΔV| <Imax×R···(1)

[0018] The multiple battery packs 12 constituting the combined battery pack 10 are connected in parallel. The multiple lithium-ion batteries 12a constituting the battery pack 12 are connected in series, in parallel, or in both series and parallel. The multiple lead-acid batteries constituting the lead-acid battery pack 16 are connected in series, in parallel, or in both series and parallel. Here, the term "lithium-ion battery" refers not only to lithium-ion battery cells but also to lithium-ion battery modules, which are composed of multiple lithium-ion battery cells connected in series, in parallel, or in both series and parallel as components of each battery pack. A spark is a spark that occurs between the positive and negative contacts of the contactor switch 12c due to discharge. Sparks can deteriorate or damage the contacts and the surrounding plastic materials. The operating voltage range refers to the voltage range within which the battery pack 12 or the lead-acid battery pack 16 can be charged and discharged. The predetermined operating voltage range is not particularly limited, but may be, for example, a range in which the voltage of each lithium-ion battery 12a cell is less than 2.90 V or more than 4.10 V.

[0019] With this configuration, the combined battery pack of the first embodiment of the present invention can have a long life because it takes into consideration measures to prevent sparks when the switch is opened and closed by connecting a lead-acid battery pack in parallel to the battery pack and reducing the voltage difference across the contactor switch after the contactor switch is opened.In addition, the combined battery pack of the first embodiment of the present invention takes into consideration measures to prevent inrush current when the switch is closed, so it can greatly reduce sparks and voltage fluctuations. The combined battery pack of the first embodiment of the present invention is basically configured as described above.

[0020] Next, a detailed description will be given of a battery connection method for a combined battery pack according to a second embodiment of the present invention. Since the battery connection method for a combined battery pack according to the second embodiment of the present invention is a battery connection method using the combined battery pack according to the first embodiment of the present invention, the same components are given the same reference numerals and their description will be omitted.

[0021] In the battery connection method for a combined battery pack according to the second embodiment of the present invention, a plurality of lithium-ion batteries 12a are first placed inside a housing (not shown) and the lithium-ion batteries 12a are connected in parallel to form a parallel group as a preliminary preparation for constructing the combined battery pack 10. Next, a lead-acid battery pack 16, which is formed by connecting a pre-calculated number of lead-acid batteries in series to each parallel group of the lithium-ion batteries 12a, is connected in parallel to the parallel group of the lithium-ion batteries 12a. At the same time, a data line 18a for measuring the voltage Va of each lithium-ion battery 12a is connected between the integrated battery management system 14 and each lithium-ion battery 12a, and a data line 18b for measuring the voltage Vb of the lead-acid battery pack 16 is connected between the integrated battery management system 14 and the lead-acid battery pack 16. Next, the integrated battery management system 14 acquires the internal impedance R' and maximum allowable current I'max of each lithium-ion battery 12a and confirms that the contactor switch 12c connected in series to each lithium-ion battery 12a is open.

[0022] After the preparation is complete, the integrated battery management system 14 repeatedly charges the combined battery pack 10 until the voltage reaches a value (first range) that is the product of the number of series-connected cells constituting each lithium-ion battery 12a and 3.95 to 4.10 V, and then discharges the combined battery pack 10 until the voltage reaches a value (second range) that is the product of the number of series-connected cells constituting each lithium-ion battery 12a and 2.90 to 3.05 V. Furthermore, during this voltage raising / lowering operation, when the voltage difference ΔV' between the voltage Va of one of the lithium-ion batteries 12a and the voltage Vb of the lead-acid battery pack 16 satisfies the following formula (2), the integrated battery management system 14 performs a battery connection operation to close the contactor switch 12c connected in series with the lithium-ion battery. The battery connection operation is then repeated for the other lithium-ion battery 12a. 0≦|ΔV´| <I´max×R´···(2)

[0023] If the lead-acid battery pack 16 is a plurality of lead-acid battery packs connected in parallel with each other, and the voltage difference between the lead-acid battery packs increases while the integrated battery management system 14 repeatedly charges and discharges the combined battery pack 10, it is preferable that the integrated battery management system 14 fully charges the combined battery pack 10 and then leaves it for 10 to 30 hours to equalize the voltages of the lead-acid battery packs. In the above explanation, A to BV means a voltage range of A volts or more and less than B volts.

[0024] Each lithium-ion battery 12a may be housed in an individual container as a battery pack 12. The means for measuring the voltage Va of each lithium-ion battery 12a is not limited to, but may be measured by a battery management system 12b provided in the individual container that houses each lithium-ion battery 12a. The means for measuring the voltage Vb of the lead-acid battery pack 16 is not limited to, but may be measured by the integrated battery management system 14.

[0025] With this configuration, the battery connection method for a combined battery pack according to the second embodiment of the present invention takes into consideration measures against sparks when the switch is opened and closed, thereby achieving a long battery life. In addition to the above effects, the battery connection method for a combined battery pack according to the second embodiment of the present invention has a simple process that allows interconnection in a short time. The battery connection method for the combined battery pack according to the second embodiment of the present invention is basically configured as described above.

[0026] Next, a detailed description will be given of a different type of battery mixed combined battery pack according to a third embodiment of the present invention. Fig. 2 is a block diagram showing a different type of battery mixed combined battery pack according to the third embodiment of the present invention.

[0027] A heterogeneous battery mixed combined battery pack 20 according to a third embodiment of the present invention includes a plurality of battery packs (22, 24) and a lead-acid battery pack 26. The plurality of battery packs (22, 24) and the lead-acid battery pack 26 have different operating voltage ranges and are connected in parallel. Each of the plurality of battery packs (22, 24) includes a corresponding plurality of lithium-ion batteries (22a, 24a) and a corresponding contactor switch (22b, 24b). The plurality of lithium-ion batteries (22a, 24a) are connected in series and parallel to each other. Each contactor switch (22b, 24b) is connected in series to the corresponding plurality of lithium-ion batteries (22a, 24a). Each contactor switch (22b, 24b) is controlled to close when the voltage of the heterogeneous battery mixed combined battery pack 20 is within the operating voltage range of the corresponding battery pack (22, 24), and is controlled to open when the voltage is outside the operating voltage range. The lead-acid battery pack 26 operates in a voltage range from the highest operating voltage to the lowest operating voltage of the heterogeneous battery mixed combined battery pack 20 .

[0028] That is, the heterogeneous battery mixed combined battery pack 20 includes a first battery pack 22, a second battery pack 24, and a lead-acid battery pack 26. The first battery pack 22, the second battery pack 24, and the lead-acid battery pack 26 have different operating voltage ranges and are connected in parallel. The first battery pack 22 includes a plurality of first lithium-ion batteries 22a (e.g., NMC) and a first contactor switch 22b. The plurality of first lithium-ion batteries 22a are connected in series and parallel to each other. The first contactor switch 22b is connected in series to the plurality of first lithium-ion batteries 22a. The second battery pack 24 includes a plurality of second lithium-ion batteries 24a (e.g., LFP) and a second contactor switch 24b. The plurality of second lithium-ion batteries 24a are connected in series and parallel to each other. The second contactor switch 24b is connected in series to the plurality of second lithium-ion batteries 24a. The lead-acid battery pack 26 is configured by connecting a plurality of lead-acid batteries 26a in series and parallel. The series and parallel connection means connecting the batteries in series with each other, in parallel with each other, or in series and parallel.

[0029] The first contactor switch 22b is controlled to close when the voltage of the heterogeneous battery mixed combined battery pack 20 is within the operating voltage range of the first battery pack 22, and is controlled to open when it is outside the operating voltage range. The second contactor switch 24b is controlled to close when the voltage of the heterogeneous battery mixed combined battery pack 20 is within the operating voltage range of the second battery pack 24, and is controlled to open when it is outside the operating voltage range. The lead-acid battery pack 26 has an operating voltage range that encompasses the range from the highest operating voltage to the lowest operating voltage of the heterogeneous battery mixed combined battery pack 20.

[0030] The first battery pack 22 preferably further includes a first battery management system 22c, an integrated battery management system 22d, and a first container 22e. In this case, the first battery management system 22c collects battery information, including the voltage, current, and temperature, of the first lithium-ion battery 22a. The integrated battery management system 22d controls the opening and closing of the first contactor switch 22b. The first container 22e houses the first lithium-ion battery 22a, the first contactor switch 22b, the first battery management system 22c, and the integrated battery management system 22d.

[0031] The second battery pack 24 preferably further includes an energy management system 24c, a power control system 24d, and a second container 24e. In this case, the energy management system 24c collects battery information, including the voltage, current, and temperature, of the second lithium-ion battery 24a and controls the opening and closing of the second contactor switch 24b. The power control system 24d converts the DC output of the heterogeneous battery mixed combined battery pack 20 into AC output. The second container 24e houses the second lithium-ion battery 24a, the second contactor switch 24b, the energy management system 24c, and the power control system 24d.

[0032] The lead-acid battery pack 26 preferably further includes a third battery management system 26b and a third container 26c. In this case, the third battery management system 26b collects battery information, including the voltage, current, and temperature, of the lead-acid battery 26a. The third container 26c houses the lead-acid battery 26a and the third battery management system 26b therein. The heterogeneous battery mixed combined battery pack 20 preferably further includes an integrated energy management system 28. In this case, the integrated energy management system 28 may transmit battery information of each lithium-ion battery and each lead-acid battery to an external device, and may also transmit the open / closed status of each contactor switch to an external device.

[0033] Next, the relationship between the operating voltage and the contactor switch will be explained. For example, suppose the operating voltage of the first battery pack 22 is in the range of 525 to 648 V, and the operating voltage of the second battery pack 24 is in the range of 635 to 731 V. In this case, when the voltage of the heterogeneous battery mixed combined battery pack 20 is less than 525 V, both the first contactor switch 22b and the second contactor switch 24b are open. When the voltage is between 525 and 635 V, the first contactor switch 22b is closed and the second contactor switch 24b is open. When the voltage is between 635 and 648 V, both the first contactor switch 22b and the second contactor switch 24b are closed. When the voltage is between 648 and 731 V, the first contactor switch 22b is open and the second contactor switch 24b is closed. When the voltage is 731 V or higher, both the first contactor switch 22b and the second contactor switch 24b are open. The number of series connections is set so that the operating voltage of the lead-acid battery pack 26 falls within a range of 525 to 731V.

[0034] With this configuration, the heterogeneous battery mixed combined battery pack of the third embodiment of the present invention has a lead-acid battery pack connected in parallel to the first battery pack and the second battery pack, and by reducing the magnitude of the voltage difference across both ends of at least one of the first contactor switch and the second contactor switch after opening the switch, measures against sparks when the switches are opened are taken into consideration, thereby achieving a long life.In addition, the heterogeneous battery mixed combined battery pack of the third embodiment of the present invention is configured by connecting multiple battery packs with different operating voltage ranges in parallel, and therefore can operate over an extremely wide voltage range. The heterogeneous battery mixed type combined battery pack of the third embodiment of the present invention is basically configured as described above.

[0035] The combined battery pack, the battery connection method thereof, and the heterogeneous battery mixed combined battery pack of the present invention have been described in detail above. However, the present invention is not limited to the above description, and various improvements and modifications may be made without departing from the spirit and scope of the present invention. [Industrial Applicability]

[0036] The combined battery pack, battery connection method thereof, and heterogeneous battery mixed combined battery pack of the present invention take into consideration measures against sparks when the switch is opened and closed, and therefore have the effect of being able to have a long life. In addition, the processing steps are simple, allowing interconnection in a short time, and are therefore industrially useful. [Explanation of symbols]

[0037] 10 Combined Battery Pack 12 Battery pack 12a Li-ion battery 12b Battery Management System 12c contactor switch 14 Integrated Battery Management System 16 lead acid battery packs 18a, 18b data lines 20. Heterogeneous battery mixed type composite battery pack 22 First battery pack 22a First lithium-ion battery 22b First contactor switch 22c 1st Battery Management System 22d Integrated Battery Management System 22e 1st Container 24 Second battery pack 24a Second lithium-ion battery 24b Second contactor switch 24c Energy Management System 24d Power Control System 24e 2nd Container 26 lead-acid battery pack 26a lead acid battery 26b Third Battery Management System 26c 3rd Container 28 Integrated Energy Management System

Claims

1. A combined battery pack including a plurality of battery packs, each containing a plurality of lithium ion batteries and further including a battery management system and a contactor switch; an integrated battery management system; and a lead-acid battery pack connected in parallel to the plurality of battery packs, the integrated battery management system controls opening and closing of the contactor switches based on battery information including voltage, current, and temperature collected from the battery management system of each battery pack; The integrated battery management system controls the combined battery pack so that, when charging or discharging the combined battery pack, if the voltage of a first battery pack among the plurality of battery packs deviates from a predetermined operating voltage range that is the same for all of the plurality of battery packs, the contactor switch of the first battery pack is opened, and controls the contactor switch of the second battery pack to close when the relationship between a voltage difference ΔV between a second battery pack among the plurality of battery packs and the lead-acid battery pack, a maximum current Imax that the second battery pack can pass, and an internal resistance R of the second battery pack satisfies the following formula (1): 0≦|ΔV|<Imax×R...(1)

2. As a preliminary step, in order to configure a combined battery pack, a plurality of lithium-ion batteries are placed inside a housing, and the lithium-ion batteries are connected in parallel to each other to form a parallel group; A lead-acid battery pack is connected in parallel to each of the parallel groups of lithium-ion batteries, the lead-acid battery pack being configured by connecting a pre-calculated number of lead-acid batteries in series with each other, and a data line for measuring a voltage Va of each lithium-ion battery is connected between an integrated battery management system and each of the lithium-ion batteries, and a data line for measuring a voltage Vb of the lead-acid battery pack is connected between the integrated battery management system and the lead-acid battery pack, The integrated battery management system acquires the internal impedance R' and the maximum allowable current I'max of each lithium ion battery in advance, and confirms that the contactor switch connected in series to each lithium ion battery is open; After the completion of the advance preparation, as a voltage raising / lowering operation, the integrated battery management system charges the combined battery pack until a voltage value in a first range set in advance is reached, and then the integrated battery management system discharges the combined battery pack until a voltage value in a second range set in advance is reached, and this is repeated; During the voltage raising and lowering operation, when a voltage difference ΔV′ between a voltage Va of one of the lithium ion batteries and a voltage Vb of the lead-acid battery pack satisfies the following formula (2), the integrated battery management system performs a battery connecting operation to close a contactor switch connected in series to the one lithium ion battery, The battery connection method for a combined battery pack includes repeating the battery connection operation for each of the lithium ion batteries with respect to another lithium ion battery. 0≦|ΔV′|<I′max×R′ (2)

3. the lead-acid battery pack is a plurality of lead-acid battery packs connected in parallel with each other, 3. The battery connection method for a combined battery pack according to claim 2, wherein, when a voltage difference between the lead-acid battery packs increases while the integrated battery management system repeatedly charges and discharges the combined battery pack, the integrated battery management system fully charges the combined battery pack and then leaves it for 10 to 30 hours to equalize the voltages of the lead-acid battery packs.

4. A heterogeneous battery mixed composite battery pack configured by connecting a plurality of battery packs having different operating voltage ranges and a lead-acid battery pack in parallel, Each of the plurality of battery packs includes a plurality of lithium ion batteries connected in series and parallel to each other, and a contactor switch connected in series to the plurality of lithium ion batteries; each contactor switch is controlled to close when the voltage of the heterogeneous battery mixed combined battery pack is within an operating voltage range of each battery pack, and is controlled to open when the voltage is outside the operating voltage range; The lead-acid battery pack operates within a voltage range from a maximum operating voltage to a minimum operating voltage of the heterogeneous battery mixed combined battery pack.