JP6724730B2 - Battery module and battery pack - Google Patents

Description

The present invention relates to a battery module and a battery pack.

In a battery module including a plurality of secondary batteries, a configuration is known in which a plurality of secondary batteries are connected in parallel when discharged to a load and a plurality of secondary batteries are connected in series when charged by a charger. For example, see Patent Documents 1 and 2. In the description below, the secondary battery may be simply referred to as a battery. In the battery module having such a configuration, a plurality of batteries can be operated for a long time at the time of discharging, and can be rapidly charged while suppressing the charging current during charging.

JP-A-6-140081 JP, 2014-193033, A

However, in the battery module configured as described above, in addition to a device (for example, a switch) for switching the series and parallel of a plurality of batteries so that the load does not operate during charging, a load for disconnecting the load from the battery module is used. Additional devices (eg switches) are required.

An object according to one aspect of the present invention is to have a configuration in which a plurality of batteries are connected in parallel during discharging and a plurality of batteries are connected in series during charging, and there is no additional device for disconnecting a load from a battery module. Another object of the present invention is to provide a battery module that can cut off the power supply to the load during charging.

A battery module, which is one mode of the present invention, includes a first battery, a second battery, a first positive electrode terminal, a second positive electrode terminal, a first discharge terminal, a second discharge terminal, and a first discharge terminal. It includes a charging terminal, a second charging terminal, a first switch, and a second switch. The first positive electrode terminal is provided on the positive electrode side of the first battery, and the first negative electrode terminal is provided on the negative electrode side of the first battery. The second positive electrode terminal is provided on the positive electrode side of the second battery, and the second negative electrode terminal is provided on the negative electrode side of the second battery. The first discharge terminal is connected to the first positive electrode terminal and the second discharge terminal is connected to the second negative electrode terminal. The first charging terminal is connected to the second positive terminal. The second charging terminal is provided so as to be connectable to the first negative electrode terminal and electrically separated from the second discharging terminal. The first switch connects the first positive electrode terminal to the second positive electrode terminal or the second negative electrode terminal. The second switch connects the first negative electrode terminal and the second negative electrode terminal or the second charging terminal.

The battery module according to one embodiment has a configuration in which a plurality of batteries are connected in parallel during discharging and a plurality of batteries are connected in series during charging, and has an additional device for disconnecting the load from the battery module. The power supplied to the load can be cut off during charging without charging.

It is a figure which shows the structural example of the battery module and battery pack according to 1st Embodiment. FIG. 6 is an exemplary flow chart of a switching process between a charging mode and a discharging mode executed by the battery pack according to the first embodiment. It is a figure which shows the exemplary relationship between the wiring of the battery module and the voltage of each terminal according to 1st Embodiment. It is a figure which shows the structural example of the battery module and battery pack according to 2nd Embodiment. It is a figure which shows the structural example of the detection circuit according to embodiment. It is a figure showing an example of connection of a plurality of battery modules according to an embodiment.

Embodiments will be described below in detail with reference to the drawings.
<First Embodiment>
FIG. 1 is a diagram showing a configuration example of a battery module and a battery pack according to the first embodiment.

The battery pack 1 is an example of the battery pack according to the embodiment. As shown in FIG. 1, the battery pack 1 includes a battery module 11.
The battery module 11 is an example of the battery module according to the embodiment. The battery module 11 includes a first battery B1, a second battery B2, a first switch S1 and a second switch S2. The battery module 11 also includes a first positive electrode terminal Tp1, a first negative electrode terminal Tn1, a second positive electrode terminal Tp2, and a second negative electrode terminal Tn2. Furthermore, the battery module 11 includes a first discharging terminal Td1, a second discharging terminal Td2, a first charging terminal Tc1, and a second charging terminal Tc2.

The first battery B1 and the second battery B2 are examples of a plurality of secondary batteries included in the battery module 11. The first battery B1 and the second battery B2 are, for example, a lithium ion battery, a nickel hydrogen battery, an electric double layer capacitor, or the like. The number of batteries included in the battery module 11 is not limited to two, and 2N (N is an integer of 1 or more) batteries may be included in the battery module 11.

The first positive electrode terminal Tp1 is provided on the positive electrode side of the first battery B1, and the first negative electrode terminal Tn1 is provided on the negative electrode side of the first battery B1. The second positive electrode terminal Tp2 is provided on the positive electrode side of the second battery B2, and the second negative electrode terminal Tn2 is provided on the negative electrode side of the second battery B2.

The first discharge terminal Td1 is always connected to the first positive electrode terminal Tp1 and the second discharge terminal Td2 is always connected to the second negative electrode terminal Tn2. The first charging terminal Tc1 is always connected to the second positive electrode terminal Tp2, and the second charging terminal Tc2 is provided so as to be connectable to and disconnectable from the first negative electrode terminal Tn1.

The battery module 11 and the load 2 are connected by connecting the first discharge terminal Td1 and the load positive electrode terminal Tlp, and connecting the second discharge terminal Td2 and the load negative electrode terminal Tln. The load positive electrode terminal Tlp and the load negative electrode terminal Tln are provided in the load 2. The load 2 may be, for example, a vehicle such as an electric forklift truck or an electric vehicle, and the battery module 11 may be mounted on the load 2.

When the first battery B1 and the second battery B2 are charged by the charger 3, the first charging terminal Tc1 and the charger positive terminal Tcp are connected via the high potential power line Lph, and the second battery The charging terminal Tc2 and the charger negative terminal Tcn are connected via the low potential power line Lpl. The charger positive electrode terminal Tcp and the charger negative electrode terminal Tcn are provided in the charger 3. With such a connection, the battery module 11 and the charger 3 are connected.

As described above, in the battery module 11, the terminal to which the load 2 is connected to the battery module 11 and the terminal to which the charger 3 is connected to the battery module 11 are separately provided. That is, the first charging terminal Tc1 is electrically separated from the first discharging terminal Td1, and the second charging terminal Tc2 is electrically separated from the second discharging terminal Td2.

The first switch S1 and the second switch S2 are configured by, for example, semiconductor switches such as MOSFET (Metal Oxide Semiconductor Field Effect Transistor) or electromagnetic relays. The first switch S1 connects the first positive electrode terminal Tp1 and the second positive electrode terminal Tp2 or the second negative electrode terminal Tn2. The second switch S2 connects the first negative electrode terminal Tn1 and the second negative electrode terminal Tn2 or the second charging terminal Tc2.

For example, when the first battery B1 and the second battery B2 are discharged to the load 2, the first switch S1 connects the first positive electrode terminal Tp1 and the second positive electrode terminal Tp2, and The switch S2 connects the first negative electrode terminal Tn1 and the second negative electrode terminal Tn2. As a result, the first battery B1 and the second battery B2 are connected in parallel via the first switch S1 and the second switch S2. Therefore, according to the battery module according to the embodiment, it is possible to operate a plurality of batteries for a long time when discharging the load.

Further, for example, when the first battery B1 and the second battery B2 are charged by the charger 3, the first switch S1 connects the first positive electrode terminal Tp1 and the second negative electrode terminal Tn2. , The second switch S2 connects the first negative electrode terminal Tn1 and the second charging terminal Tc2. As a result, the first battery B1 and the second battery B2 are connected in series via the first switch S1 and the second switch S2. Therefore, according to the battery module according to the embodiment, it is possible to rapidly charge a plurality of batteries while suppressing the charging current flowing in the charging path.

Further, as described above, in the battery module 11, the terminal to which the load 2 is connected to the battery module 11 and the terminal to which the charger 3 is connected to the battery module 11 are separately provided. Therefore, the load 2 and the charger 3 are indirectly connected via the battery module 11. Then, in the battery module 11, when the first battery B1 and the second battery B2 are charged by the charger 3, the first discharge terminal Td1 and the second discharge terminal Td2 are connected to the first switch. They are connected via S1 and have the same potential. That is, the load 2 is not supplied with electric power from the first battery B1 and the second battery B2, or from the charger 3. Therefore, according to the battery module according to the embodiment, the electric power supplied to the load can be cut off during charging without an additional device for disconnecting the load from the battery module. Then, according to the battery module according to the embodiment, it is possible to prevent the load from operating by the power supplied from the plurality of batteries and/or the charger while the plurality of batteries are being charged.

Next, the battery pack 1 further includes a controller 12 and a third switch S3.
The control unit 12 is configured by, for example, a CPU (Central Processing Unit), a multi-core CPU, a programmable device (FPGA (Field Programmable Gate Array), PLD (Programmable Logic Device), or the like). The control unit 12 controls the entire battery pack 1. Further, the control unit 12 communicates with the charger 3 so that the first battery B1 and the second battery B2 are charged to a predetermined capacity.

The third switch S3 is composed of, for example, a semiconductor switch such as MOSFET or an electromagnetic relay. In the configuration example shown in FIG. 1, the third switch S3 is provided on the low-potential power line Lpl between the second charging terminal Tc2 and the charger negative terminal Tcn of the charger 3. Note that, unlike the configuration example shown in FIG. 1, the third switch S3 may be provided on the high-potential power line Lph between the positive electrode side of the second battery B2 and the charger positive electrode terminal Tcp of the charger 3. Good. That is, the third switch S3 may be provided on the high potential power line Lph between the first charging terminal Tc1 and the charger positive electrode terminal Tcp. Alternatively, it may be provided on the high-potential power line Lph closer to the second positive electrode terminal Tp2 than the first charging terminal Tc1. As described above, the third switch S3 may be provided on the path between the battery module 11 and the charger 3 through which the charging current flows.

For example, when the first battery B1 and the second battery B2 are charged by the charger 3, or when the first battery B1 and the second battery B2 are discharged to the load 2, the control unit 12 will be described below. Switch control. FIG. 2 is an exemplary flow chart of the switching process between the charge mode and the discharge mode executed by the battery pack according to the first embodiment. FIG. 3 is a diagram showing an exemplary relationship between the wiring of the battery module according to the first embodiment and the voltage of each terminal. In the example shown in FIG. 3, the full charge voltage of the first battery B1 and the second battery B2 is 48 [V], but any voltage other than 48 [V] may be used. Good.

During the discharge mode in which the first battery B1 and the second battery B2 discharge to the load 2, the battery module 11 is wired as in state A (FIG. 3). That is, the first switch S1 connects the first positive electrode terminal Tp1 and the second positive electrode terminal Tp2, and the second switch S2 connects the first negative electrode terminal Tn1 and the second negative electrode terminal Tn2. There is. The third switch S3 is open. When shifting the first battery B1 and the second battery B2 from the discharging mode to the charging mode, the control unit 12 executes a process as shown in FIG. 2A before the charging from the charger 3 is started.

First, the control unit 12 switches the second switch S2 so that the first negative terminal Tn1 and the second charging terminal Tc2 are connected (step S101). As a result, the wiring of the battery module 11 is changed from the state A to the state B (FIG. 3). Next, the controller 12 switches the first switch S1 so that the first positive electrode terminal Tp1 and the second negative electrode terminal Tn2 are connected (step S102). As a result, the wiring of the battery module 11 is further changed from the state B to the state C (FIG. 3).

In this way, the wiring of the battery module 11 is changed in the order of state A→state B→state C. According to this change in order, for example, the first positive electrode terminal Tp1 and the second negative electrode terminal Tn2 are connected by the first switch S1, and the second negative electrode terminal Tn2 and the first negative electrode terminal Tn1 are connected to each other. It is possible to prevent the first battery B1 from being short-circuited by being connected by the second switch S2.

Furthermore, after switching the first switch S1 in step S102, the control unit 12 closes the third switch (step S103). If the third switch is closed while the battery module 11 is wired as in the state B, a high charging voltage (for example, 96 [V] is applied to the load 2 that operates at low voltage (for example, 48 [V]). ]) is applied from the charger 3, and a problem may occur in the load 2. However, as described above, since the third switch is closed after the wiring of the battery module 11 is changed from the state B to the state C, such a failure can be prevented from occurring.

After performing the series of processes in steps S101 to S103, the control unit 12 starts charging the first battery B1 and the second battery B2 through communication with the charger 3.
On the other hand, during the charging mode in which the first battery B1 and the second battery B2 are charged by the charger 3, the battery module 11 is wired as in the state C. That is, the first switch S1 connects the first positive electrode terminal Tp1 and the second negative electrode terminal Tn2, and the second switch S2 connects the first negative electrode terminal Tn1 and the second charging terminal Tc2. There is. Also, the third switch S3 is closed. When shifting the first battery B1 and the second battery B2 from the charge mode to the discharge mode, the control unit 12 executes the process shown in FIG. 2B before starting the discharge to the load 2.

First, before switching the first switch S1 in step S202, the control unit 12 opens the third switch (step S201). Next, the control unit 12 switches the first switch S1 so that the first positive electrode terminal Tp1 and the second positive electrode terminal Tp2 are connected (step S202). As a result, the wiring of the battery module 11 is changed from the state C to the state B. Further, the control unit 12 switches the second switch S2 so that the first negative electrode terminal Tn1 and the second negative electrode terminal Tn2 are connected (step S203). As a result, the wiring of the battery module 11 is changed from the state B to the state A.

In this way, the wiring of the battery module 11 is changed in the order of state C→state B→state A. By changing the order, it is possible to prevent the first battery B1 from being short-circuited as described above.

Further, if the wiring of the battery module 11 is changed from the state C to the state B while the third switch is closed, the high charging voltage from the charger 3 still connected to the battery module 11 becomes low. The load is applied to the operating load 2, and there is a possibility that the load 2 may malfunction. However, as described above, since the third switch is opened before the wiring of the battery module 11 is changed from the state C to the state B, such a defect can be prevented from occurring.
<Second Embodiment>
FIG. 4 is a diagram showing a configuration example of the battery module and the battery pack according to the second embodiment. 4, the same components as those shown in FIG. 1 are designated by the same reference numerals as those shown in FIG. As shown in FIG. 4, the battery pack 4 includes a battery module 11. Further, the battery pack 4 includes a control unit 42 instead of the control unit 12. Further, the battery pack 4 includes a voltage sensor V and a detection circuit D.

The voltage sensor V is composed of, for example, a voltage detection IC (Integrated Circuit) or the like. The voltage sensor V measures the voltage value of the first charging terminal Tc1. For example, as shown in FIG. 3, when the first switch S1 connects the first positive electrode terminal Tp1 and the second positive electrode terminal Tp2 as in the state A or the state B, the first charging terminal The voltage of Tc1 is measured to be relatively low voltage of 48 [V]. On the other hand, as in the state C, the first switch S1 connects the first positive terminal Tp1 and the second negative terminal Tn2, and the second switch S2 connects the first negative terminal Tn1 and the second charging terminal. When Tc2 is connected, the voltage of the first charging terminal Tc1 is measured to be a relatively high voltage of 96 [V]. The measured voltage value is input to the control unit 42.

The detection circuit D detects a conduction state between the first negative electrode terminal Tn1 and the second charging terminal Tc2. The detection circuit D is configured, for example, as shown in FIG. FIG. 5 is a diagram illustrating a configuration example of the detection circuit according to the embodiment. In the configuration example shown in FIG. 5, the detection circuit D includes a first pull-up resistor R1, a second pull-up resistor R2, a light emitting element LED, and a light receiving element PD. The light emitting element LED and the light receiving element PD form a photo coupler.

One end of the first pull-up resistor R1 is connected to a predetermined voltage source Vs (for example, 5 [V]), and the other end of the first pull-up resistor R1 is connected to one end (anode) of the light emitting element LED. The other end (cathode) of the light emitting element LED is connected to the first negative electrode terminal Tn1. The predetermined voltage source Vs may be generated by the output voltage from the first battery B1 and the second battery B2.

Further, one end of the second pull-up resistor R2 is connected to the voltage source Vs, and the other end of the second pull-up resistor R2 is connected to the input terminal Tin of the control unit 42 and one end (collector) of the light receiving element PD. It The other end (emitter) of the light receiving element PD is connected to the ground.

For example, when the second switch S2 connects the first negative electrode terminal Tn1 and the second negative electrode terminal Tn2 as in the state A, no current flows in the light emitting element LED and the light emitting element LED does not emit light. As a result, the light receiving element PD does not conduct, and an OFF signal having a relatively high signal level is input to the input terminal Tin of the control unit 42. On the other hand, when the second switch S2 connects the first negative terminal Tn1 and the second charging terminal Tc2 as in the state B or the state C, a current flows through the light emitting element LED and the light emitting element LED emits light. .. As a result, the light receiving element PD becomes conductive, and an ON signal having a relatively low signal level is input to the input terminal Tin of the control unit 42. In this way, the detection circuit D detects the conduction state between the first negative electrode terminal Tn1 and the second charging terminal Tc2.

The control unit 42 is configured by a CPU, a multi-core CPU, a programmable device (FPGA, PLD, etc.), or the like, and controls the entire battery pack 4. The control unit 42 executes the same process as the control unit 12, and determines whether or not the first switch S1 and the second switch S2 are welded.

For example, when the voltage value measured by the voltage sensor V changes from high voltage to low voltage or from low voltage to high voltage when the switching operation of the first switch S1 is executed, the control unit 42 causes the first switch S1 to change. It is determined that welding has not occurred. On the other hand, when the voltage value measured by the voltage sensor V does not change from high voltage to low voltage or from low voltage to high voltage when the switching operation of the first switch S1 is performed, the control unit 42 causes the first switch S1 to change. It is determined that welding has occurred.

When the control signal input to the input terminal Tin changes from the ON signal to the OFF signal or from the OFF signal to the ON signal when the switching operation of the second switch S2 is executed, the control unit 42 It is determined that the second switch S2 is not welded. On the other hand, when the control signal input to the input terminal Tin does not change from the ON signal to the OFF signal or from the OFF signal to the ON signal when the switching operation of the second switch S2 is executed, the control unit 42 It is determined that the second switch S2 is welded.

When welding occurs in at least one of the first switch S1 and the second switch S2, the control unit 42 switches the discharge mode to the charge mode (FIG. 2A) and the charge mode to the discharge mode. Is not executed (FIG. 2(B)). Further, the control unit 42 may notify the load 2 and the charger 3 that welding has occurred.

Whether or not the first switch S1 is welded may be determined when the switching process of the first switch S1 is executed. That is, for example, whether or not the first switch S1 is welded may be determined when the process of step S102 (FIG. 3A) or step S202 (FIG. 3B) is performed. Similarly, the presence or absence of welding of the second switch S2 may be determined when the switching process of the second switch S2 is executed. That is, for example, whether or not the second switch S2 is welded may be determined when the process of step S101 (FIG. 3A) or step S203 (FIG. 3B) is performed. According to such a processing procedure, it is not necessary to switch the first switch S1 or the second switch S2 only for determining the presence/absence of welding, so that the processing for determining the presence/absence of welding can be made efficient.

The battery module and the battery pack according to the second embodiment can also achieve the same effects as those of the battery module and the battery pack according to the first embodiment. Further, according to the battery module and the battery pack according to the second embodiment, since the mode switching is not executed when the switch is welded, it is possible to reliably switch the charging mode and the discharging mode.

The present invention is not limited to the above embodiments, and various improvements and changes can be made without departing from the gist of the present invention.
For example, in the configuration example shown in FIGS. 1 and 4, one battery module 11 is included in the battery pack 1, but two or more battery modules 11 according to the embodiment are batteries according to the embodiment. It may be included in the pack. In that case, the plurality of battery modules 11 according to the embodiment may be connected to each other as shown in FIG. 6, for example. FIG. 6 is a diagram showing a connection example of a plurality of battery modules according to the embodiment.

The first battery module 11-1 and the second battery module 11-2 shown in FIG. 6 are the battery module 11 described above with reference to FIGS. 1 to 5. As shown in FIG. 6, the second charging terminal Tc2 of the first battery module 11-1 and the first charging terminal Tc1 of the second battery module 11-2 are connected. The second discharge terminal Td2 of the first battery module 11-1 and the first discharge terminal Td1 of the second battery module 11-2 are connected or disconnected by the fourth switch S4.

The fourth switch S4 is composed of a semiconductor switch such as MOSFET, an electromagnetic relay, or the like, and is used in the embodiment such as the battery pack 1 or 4 together with the first battery module 11-1 and the second battery module 11-2. Included in the battery pack according to.

When the first battery B1 and the second battery B2 of the first battery module 11-1 and the second battery module 11-2, respectively, are discharged, the fourth switch S4 operates as follows. That is, the fourth switch S4 connects the second discharge terminal Td2 of the first battery module 11-1 and the first discharge terminal Td1 of the second battery module 11-2. On the other hand, when the first battery B1 and the second battery B2 of the first battery module 11-1 and the second battery module 11-2 are charged, the fourth switch S4 operates as follows. .. That is, the fourth switch S4 disconnects the second discharge terminal Td2 of the first battery module 11-1 and the first discharge terminal Td1 of the second battery module 11-2. The fourth switch S4 may be switched by a control unit such as the control unit 12 or 41 included in the battery pack according to the embodiment.

If the plurality of battery modules according to the embodiment are configured to be included in the battery pack according to the embodiment, the battery pack according to the embodiment can correspond to a load operating at a higher voltage.

1, 4 Battery pack 2 Load 3 Charger 11 Battery module 12, 42 Control unit B1 First battery B2 Second battery D Detection circuit Lph High potential power line Lpl Low potential power line LED Light emitting element PD Light receiving element R1 First pull Up resistor R2 Second pull up resistor S1 First switch S2 Second switch S3 Third switch S4 Fourth switch Tc1 First charging terminal Tc2 Second charging terminal Tcn Charger negative electrode terminal Tcp Charger positive electrode Terminal Td1 First discharge terminal Td2 Second discharge terminal Tin Input terminal Tln Load negative terminal Tlp Load positive terminal Tn1 First negative terminal Tn2 Second negative terminal Tp1 First positive terminal Tp2 Second positive terminal V Voltage Sensor Vs Voltage source

Claims (9)

A first battery,
A second battery,
A first positive electrode terminal provided on the positive electrode side of the first battery;
A first negative electrode terminal provided on the negative electrode side of the first battery;
A second positive electrode terminal provided on the positive electrode side of the second battery;
A second negative electrode terminal provided on the negative electrode side of the second battery;
A first discharge terminal connected to the first positive electrode terminal;
A second discharge terminal connected to the second negative electrode terminal;
A first charging terminal connected to the second positive terminal,
A second charging terminal provided so as to be connectable to the first negative electrode terminal and electrically separated from the second discharging terminal;
A first switch connecting the first positive electrode terminal and the second positive electrode terminal or the second negative electrode terminal;
A battery module comprising a second switch connecting the first negative electrode terminal and the second negative electrode terminal or the second charging terminal. The battery module according to claim 1, wherein
When the first battery and the second battery are discharged, the first switch connects the first positive electrode terminal and the second positive electrode terminal, and the second switch connects the first positive electrode terminal and the second positive electrode terminal. Connecting the negative electrode terminal of 1 and the second negative electrode terminal,
When the first battery and the second battery are charged, the first switch connects the first positive electrode terminal and the second negative electrode terminal, and the second switch is A battery module for connecting a first negative electrode terminal and the second charging terminal. The battery module according to claim 2,
When shifting the first battery and the second battery from the discharge mode to the charging mode, first set the second switch so that the first negative terminal and the second charging terminal are connected. A battery pack comprising: a controller that switches and switches the first switch next so that the first positive electrode terminal and the second negative electrode terminal are connected. The battery module according to claim 2,
When the first battery and the second battery are shifted from the charge mode to the discharge mode, first the first switch is connected so that the first positive electrode terminal and the second positive electrode terminal are connected. A battery pack including: a controller that switches and switches the second switch next so that the first negative electrode terminal and the second negative electrode terminal are connected. The battery pack according to claim 3,
A power line between the positive electrode side of the second battery and a positive electrode terminal of the charger or a third switch provided on a power line between the second charging terminal and a negative electrode terminal of the charger,
The battery pack in which the control unit closes the third switch after switching the first switch. The battery pack according to claim 4, wherein
A power line between the positive electrode side of the second battery and a positive electrode terminal of the charger or a third switch provided on a power line between the second charging terminal and a negative electrode terminal of the charger,
The control unit is a battery pack in which the third switch is opened before switching the first switch. It is a battery pack as described in any one of Claims 3-6, Comprising:
The control unit determines whether or not the first switch is welded according to a voltage value of the first charging terminal, and determines whether or not the first negative terminal and the second charging terminal are electrically connected to each other. A battery pack that determines whether or not a switch is welded. A first battery module and a second battery module which are the battery module according to claim 1 or 2;
A fourth switch for connecting or disconnecting the second discharge terminal of the first battery module and the first discharge terminal of the second battery module,
A battery pack in which the second charging terminal of the first battery module and the first charging terminal of the second battery module are connected. The battery pack according to claim 8,
When the first battery and the second battery of each of the first battery module and the second battery module are discharged, the fourth switch is configured to operate the second switch of the first battery module. The discharge terminal of the second battery module and the first discharge terminal of the second battery module are connected,
When the first battery and the second battery of each of the first battery module and the second battery module are charged, the fourth switch is configured to operate the first switch of the first battery module. A battery pack that disconnects the second discharge terminal and the first discharge terminal of the second battery module.

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