JP2017124800A - Power supply device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow a lithium ion battery to be used as power supply for a startup of a vehicle even at an ultralow temperature.SOLUTION: A power supply device comprises a first battery, a discharge load, a first switch, a second battery, a second switch, a measurement section and a control section. The first battery has a lithium ion battery capable of supplying electric power to a first load. The discharge load is connected to the first battery, and causes the electric power stored in the first battery to be discharged. The first switch can switch connection and disconnection of the discharge load and the first battery. The second battery is connected to the first battery in parallel. The second switch can switch parallel connection and disconnection of the first battery and the second battery. The measurement section measures a temperature of the first battery. The control section executes first processing until the temperature of the first battery reaches a prescribed temperature, and supplies the electric power at least from the first battery to the first load when the temperature of the first battery reaches the prescribed temperature.SELECTED DRAWING: Figure 1

Description

  Embodiments described herein relate generally to a power supply apparatus.

  As a power source for starting a vehicle, a 12V lead battery is generally used. However, the lead battery has a problem of environmental impact, heavy weight, poor charging performance, and periodic replacement due to deterioration. Therefore, it has been studied to use a lithium ion battery as a battery for starting the vehicle.

Japanese Patent No. 5092810

  However, non-aqueous batteries such as lithium ion batteries have excellent input / output performance at room temperature and are lightweight, but solution resistance, charge transfer resistance, and diffusion resistance increase at extremely low temperatures. As a power source, there is a part lower in performance than a lead battery.

  The power supply device of the embodiment includes a first battery, a discharge load, a first switch, a second battery, a second switch, a measurement unit, and a control unit. The first battery includes a lithium ion battery that can supply power to the first load. The discharge load is connected to the first battery and discharges the electric power stored in the first battery. The first switch can switch connection and disconnection between the discharge load and the first battery. The second battery is connected in parallel with the first battery. The second switch can switch between parallel connection and disconnection of the first battery and the second battery. The measurement unit measures the temperature of the first battery. The controller executes the first process until the temperature of the first battery reaches a predetermined temperature, and when the temperature of the first battery reaches the predetermined temperature, supplies power from at least the first battery to the first load. In the first process, the first switch is switched to connect the first battery and the discharge load to discharge the electric power stored in the first battery, and the battery voltage of the first battery becomes equal to or lower than the first predetermined voltage. In this case, after switching the first switch to disconnect the discharge load from the first battery, the second switch is switched to connect the first battery and the second battery in parallel to supply power from the second battery to the first battery. The first battery is charged until the battery voltage of the first battery reaches a second predetermined voltage higher than the first predetermined voltage.

FIG. 1 is a diagram illustrating an example of a configuration of a power supply system according to the first embodiment. FIG. 2 is a diagram illustrating an example of OCV characteristics of the first battery and the second battery included in the power supply device according to the first embodiment. FIG. 3 is a diagram illustrating an example of changes in current and voltage during discharging and charging of the first battery and the second battery included in the power supply device according to the first embodiment at an extremely low temperature. FIG. 4 is a diagram illustrating an example of the relationship between the discharge resistance of the first battery included in the power supply device according to the first embodiment and the ambient temperature. FIG. 5 shows an example of changes in the battery voltage, current, and temperature of the first battery and an example of changes in the battery voltage and current of the second battery during the temperature raising process in the power supply device according to the first embodiment. FIG. FIG. 6 is a flowchart illustrating an example of a flow of temperature increase processing for the first battery in the power supply device according to the first embodiment. FIG. 7 is a diagram illustrating an example of a configuration of a power supply system according to the second embodiment.

  Hereinafter, a power supply system to which the power supply device according to the present embodiment is applied will be described with reference to the accompanying drawings.

(First embodiment)
FIG. 1 is a diagram illustrating an example of a configuration of a power supply system according to the first embodiment. As shown in FIG. 1, the power supply system according to the present embodiment is mounted on a vehicle such as an automobile, and supplies power to various loads that the vehicle has. Specifically, the power supply system includes a generator D, an engine E, a starter S, an auxiliary machine H, and a power supply device 1.

  The generator D supplies the generated power to the engine E, the auxiliary machine H, and the power supply device 1. The engine E generates power for running the vehicle. The engine E rotates the generator D when power generation is required. The starter S (an example of a first load) is an electric motor that is supplied with electric power from the power supply device 1 and starts the engine E. The auxiliary machine H is a headlamp, a blinker (direction indicator), an electric pump, an ECU (Engine Control Unit) that performs vehicle control, and the like. Power is supplied from at least one of the generator D and the power supply device 1.

  The power supply device 1 supplies power to various loads such as a starter S and an auxiliary machine H. Specifically, as shown in FIG. 1, the power supply device 1 includes a control unit 101, a first battery B1, a second battery B2, a discharge load 102, a temperature sensor 103, a first switch SW1, A second switch SW2 and a third switch SW3 are included. The first battery B1 is a power source that supplies power to the starter S, such as a lithium ion battery. In the present embodiment, a battery having a smaller capacity and excellent regenerative performance than the second battery B2 described later is used as the first battery B1. For example, the first battery B1 is an assembled battery of a lithium ion battery having, as a negative electrode, lithium titanate having excellent regeneration performance. The second battery B2 is connected in parallel with the first battery B1. In the present embodiment, the second battery B2 uses a battery having a larger capacity than the first battery B1, such as a lead battery or a lithium ion battery.

  The discharge load 102 is connected to the first battery B1 and can discharge the electric power stored in the first battery B1. For example, the discharge load 102 is a heater that generates heat by the electric power discharged from the first battery B1 and can warm the first battery B1. The temperature sensor 103 (an example of a measurement unit) measures the temperature of the first battery B1. The first switch SW1 is a switch that can switch connection and disconnection between the discharge load 102 and the first battery B1. The second switch SW2 is a switch that can switch between parallel connection and disconnection of the first battery B1 and the second battery B2. The third switch SW3 is a switch that can switch connection and disconnection between the first battery B1 and the starter S.

  The control unit 101 monitors the state of the first battery B1 and the second battery B2, such as the voltage and temperature, controls the supply of power from the power supply device 1 to various loads, and controls the power supply device 1 as a whole.

  Here, the characteristics of the first battery B1 and the second battery B2 included in the power supply device 1 according to the present embodiment will be described with reference to FIGS. FIG. 2 is a diagram illustrating an example of OCV characteristics of the first battery and the second battery included in the power supply device according to the first embodiment. FIG. 3 is a diagram illustrating an example of changes in current and voltage during discharging and charging of the first battery and the second battery included in the power supply device according to the first embodiment at an extremely low temperature. FIG. 4 is a diagram illustrating an example of the relationship between the resistance of the first battery and the ambient temperature included in the power supply device according to the first embodiment.

  FIG. 2 is an example of this embodiment, but shows the OCV (Open Circuit Voltage) of the first battery B1 and the second battery B2, and is displayed so that the OCV crosses at about 12.8V. It is. In this embodiment, since it considers that the 2nd battery B2 is a lead battery, 12.8V is in the state where it discharged from the full charge vicinity of the lead battery or a little from full charge. In the present embodiment, the control unit 101 has an OCV of about 12.8 V, connects the first battery B1 and the second battery B2 in parallel, and starts from the first battery B1 and the second battery B2 to the starter S or auxiliary machine H. It is the structure which can supply electric power to various loads, such as.

  FIG. 3 shows the operation of the power supply device 1 at an extremely low temperature, and shows the problems to be solved in the present embodiment. Specifically, FIG. 3 shows an assembled battery in which a first battery B1, which is an assembled battery of a lithium ion battery using lithium titanate as a negative electrode, and a lead battery having a discharge capacity larger than that of the first battery B1 are connected in parallel. It shows changes in current and voltage when the second battery B2 is discharged or charged at an extremely low temperature (for example, −30 ° C.). Specifically, it is understood that when discharging at 45 A for about 60 s, the current discharged from the second battery B2 (about 35 A) is larger than the current discharged from the first battery B1 (about 15 A). That is, the first battery B1 has a large discharge resistance at an extremely low temperature, and the dischargeable current is smaller than that of the second battery B2. Furthermore, even when the first battery B1 and the second battery B2 are discharged at 300 A at an extremely low temperature for about 1 s, the current discharged from the second battery B2 (about 230 A) is the current discharged from the first battery B1. It can be seen that it is larger than (70A). On the other hand, when the first battery B1 and the second battery B2 are charged at 80A at an extremely low temperature, the current flowing through the first battery B1 is larger than the current flowing through the second battery B2.

  From the above, the first battery B1 has a current that flows during discharge at a very low temperature, which is smaller than that of the second battery B2, and cannot supply sufficient power to the external load (for example, the starter S). Since it is larger than the second battery B2, charging is possible. On the other hand, the second battery B2 has a current that can be flowed at the time of discharge larger than that of the first battery B1 at a very low temperature. For this reason, when a lithium ion battery is used as a power source for starting a vehicle, the discharge capacity at extremely low temperatures is inferior. Therefore, in order to use a lithium ion battery as a power source for starting a vehicle even at a very low temperature, it is connected in parallel. It is necessary to increase the number of lithium ion batteries, and there is a problem that the weight of the power supply device 1 increases.

  FIG. 4 shows the resistance values (charge resistance, discharge resistance) of the battery cells included in the first battery B1. The battery cell included in the first battery B1 has a resistance at an ambient temperature of −30 ° C., which is an extremely low temperature, of 15 times or more as compared with a resistance at an ambient temperature of 25 ° C. both during charging and discharging. Therefore, the battery cell included in the first battery B1 has a limited increase in resistance value if the ambient temperature is −10 ° C. (about three times the resistance when the ambient temperature is 25 ° C.). If the temperature of the first battery B1 can be raised to about 20 ° C. in a short time at an extremely low temperature, the battery can be used as a power source for starting the vehicle (that is, a power source for the starter S). Show.

  In the present embodiment, based on the characteristics of the first battery B1 and the second battery B2 shown in FIGS. 3 and 4, the control unit 101 is instructed to start the engine E by pressing the engine start button of the vehicle. Until the temperature of the first battery B1 measured by the temperature sensor 103 reaches the predetermined temperature T1, the temperature increase process (an example of the first process) of the first battery B1 is executed, and the temperature of the first battery B1 is the predetermined temperature. When T1 is reached, power is supplied from at least the first battery B1 to the starter S. Here, when the first battery B1 is discharged, the predetermined temperature T1 is a short time (in this embodiment, shorter than the time required for starting the starter S), and the battery voltage of the first battery B1 is predetermined. The temperature does not reach the lower limit voltage of the allowable use voltage range (for example, −10 ° C.). The predetermined allowable use voltage range is a discharge-side voltage range in which use of the first battery B1 is permitted.

  In the temperature raising process described above, the first switch SW1 is switched to connect the discharge load 102 and the first battery B1 to discharge the electric power stored in the first battery B1, and the battery voltage of the first battery B1 is changed to the first voltage. 1 When the voltage is lower than the predetermined voltage V1, the first switch SW1 is switched to disconnect the first battery B1 from the discharge load 102, and then the second switch SW2 is switched to switch the first battery B1 and the second battery B2. The power is supplied in parallel from the second battery B2 to the first battery B1 until the battery voltage of the first battery B1 reaches the second predetermined voltage V2 (or from the second battery B2 to the first battery B1). This is a process of charging the first battery B1 (until the flowing current is equal to or less than a predetermined current value or reaches a predetermined time). Here, the first predetermined voltage V1 is a voltage within a predetermined allowable use voltage range. In the present embodiment, the first predetermined voltage V1 is a lower limit voltage on the discharge side of a predetermined usable allowable voltage range. The second predetermined voltage V2 is a voltage within a predetermined allowable use voltage range, and is higher than the first predetermined voltage V1.

  According to the above-described temperature raising process, the first battery B1 is generated by performing internal heat generation of the first battery B1 due to the discharge from the first battery B1 to the discharge load 102 and charging the first battery B1 by the second battery B2. Due to the internal heat generation, the inside of the battery cell included in the first battery B1 can be efficiently warmed up. By repeating the charging and discharging, the temperature can be raised in a short time. As a result, the first battery B1 can be raised in a short time to a temperature at which sufficient discharge capability can be realized, and the lithium ion battery can be used as a power source for starting a vehicle even in a cryogenic environment. Can do. Moreover, according to the above-mentioned temperature rising process, when using a lithium ion battery as a power source of the starter S, without increasing the battery capacity of the lithium ion battery or increasing the parallel number of the lithium ion batteries, Since the starter S can be started at an extremely low temperature, it is possible to prevent the power supply for the vehicle from increasing in size.

  Next, an example of the temperature raising process of the first battery B1 in the power supply device 1 according to the present embodiment will be described with reference to FIG. Fig.5 (a) is a figure which shows an example of the battery voltage of the 1st battery at the time of the temperature rising process in the power supply device concerning 1st Embodiment, an electric current, and a change of temperature. FIG. 5B is a diagram illustrating an example of changes in the battery voltage and current of the second battery during the temperature increasing process in the power supply device according to the first embodiment.

  When the start of the engine E is instructed, the control unit 101 first turns on the first switch SW1 to connect the first battery B1 and the discharge load 102 as shown in FIG. The power stored in B1 is discharged to the discharge load 102 to cause the first battery B1 to self-heat. Thereafter, as shown in FIG. 5A, the control unit 101 applies the first battery B1 to the discharge load 102 until the battery voltage of the first battery B1 becomes equal to or lower than a first predetermined voltage V1 (for example, 9V). Continue discharging.

  Thereafter, when the battery voltage of the first battery B1 becomes equal to or lower than the first predetermined voltage V1, the control unit 101 switches the first switch SW1 to OFF and sets the first switch SW1 to OFF as shown in FIGS. 5 (a) and 5 (b). The second switch SW2 is turned on to connect the first battery B1 and the second battery B2 in parallel, and power is supplied from the second battery B2 to the first battery B1 to charge the first battery B1. Thereafter, as illustrated in FIG. 5A, the control unit 101 performs the second battery B2 with respect to the first battery B1 until the battery voltage of the first battery B1 reaches a second predetermined voltage V2 (for example, 12.5 V). Continue to supply power from Thereafter, when the battery voltage of the first battery B1 reaches the second predetermined voltage V2, the control unit 101 switches off the second switch SW2 to disconnect the parallel connection between the first battery B1 and the second battery B2. Then, the first switch SW1 is turned on again to discharge the electric power stored in the first battery B1 to the discharge load 102. As shown in FIG. 5A, the control unit 101 repeats the above temperature raising process until the temperature T of the first battery B1 reaches a predetermined temperature T1 (for example, −10 ° C.). That is, in the temperature raising process, after the battery voltage of the first battery B1 reaches the second predetermined voltage V2, the second switch SW2 is switched to disconnect the connection between the first battery B1 and the second battery B2. The discharge of the electric power stored in the first battery B1 and the charging of the first battery B1 are repeated until the temperature of B1 reaches a predetermined temperature T1.

  Next, with reference to FIG. 6, an example of the flow of temperature increase processing for the first battery B1 in the power supply device 1 according to the present embodiment will be described. FIG. 6 is a flowchart illustrating an example of a flow of temperature increase processing of the first battery B1 in the power supply device according to the first embodiment.

  When starting the engine E is instructed, the control unit 101 switches off the second switch SW2 and disconnects the parallel connection between the first battery B1 and the second battery B2 (step S601). Next, the control unit 101 controls the temperature sensor 103 to measure the temperature T of the first battery B1 (step S602). Further, the control unit 101 compares the measured temperature T of the first battery B1 with the predetermined temperature T1, and determines whether or not the temperature T of the first battery B1 is equal to or lower than the predetermined temperature T1 (step). S602).

  When the temperature T of the first battery B1 is higher than the predetermined temperature T1 (step S602: No), the control unit 101 supplies power from at least the first battery B1 to the starter S among the first battery B1 and the second battery B2. And starter S is started (step S604). Specifically, when supplying power from only the first battery B1 to the starter S, the control unit 101 switches off the second switch SW2 to connect the first battery B1 and the second battery B2 in parallel. In the disconnected state, the third switch SW3 is turned on to supply power from the first battery B1 to the starter S. On the other hand, when supplying power from both the first battery and the second battery B2 to the starter S, the control unit 101 switches on the second switch SW2 to connect the first battery B1 and the second battery B2 in parallel. In a connected state, the third switch SW3 is switched on to supply power to the starter S from both the first battery B1 and the second battery B2.

  On the other hand, when the temperature T of the first battery B1 is equal to or lower than the predetermined temperature T1 (step S602: Yes), the control unit 101 switches on the first switch SW1 to connect the first battery B1 and the discharge load 102. Then, the electric power stored in the first battery B1 is discharged to the discharge load 102 to cause the first battery B1 to generate heat (step S603). Furthermore, as an example of the present embodiment, a heater is used for the discharge load 102, and the temperature of the first battery B1 is also increased by the heat generated by the heater. As a result, the temperature of the first battery B1 can be increased by the heat generation of the discharge load 102 in addition to the heat generation inside the cell due to charging / discharging of the first battery B1, so the first battery B1 can be heated in a shorter time. The temperature can be raised. Next, the control unit 101 compares the battery voltage of the first battery B1 with the first predetermined voltage V1, and determines whether or not the battery voltage of the first battery B1 is equal to or lower than the first predetermined voltage V1 (step). S605).

  When the battery voltage of the first battery B1 is higher than the first predetermined voltage V1 (step S605: No), the control unit 101 returns to step S603 and discharges the electric power stored in the first battery B1 to the discharge load 102. continue. On the other hand, when the battery voltage of the first battery B1 is equal to or lower than the first predetermined voltage V1 (step S605: Yes), the control unit 101 switches off the first switch SW1 to connect the first battery B1 and the discharge load 102. The first battery B1 and the second battery B2 are connected in parallel by supplying the second battery SW1 to the first battery B1 by switching the second switch SW2 to ON. B1 is charged (step S606).

  Next, the control unit 101 determines whether or not the battery voltage of the first battery B1 has become equal to or higher than the second predetermined voltage V2 (step S607). Alternatively, the control unit 101 determines whether the charging current that is the current flowing from the second battery B2 to the first battery B1 has converged to a predetermined current value, or whether the charging time has reached a predetermined time. to decide. When the battery voltage of the first battery B1 is lower than the second predetermined voltage V2 (step S607: No), the control unit 101 returns to step S606 and continues to supply power from the second battery B2 to the first battery B1. .

  On the other hand, when the battery voltage of the first battery B1 is equal to or higher than the second predetermined voltage V2 (step S607: Yes), the control unit 101 returns to step S601, switches the second switch SW2 to OFF, and switches the first battery B1. And the second battery B2 are disconnected in parallel. The control unit 101 repeats the above temperature raising process until the temperature T of the first battery B1 becomes higher than the predetermined temperature T1.

  Thus, according to the power supply system according to the first embodiment, the lithium ion battery can be used as a power supply for starting the vehicle even at an extremely low temperature. Moreover, according to the above temperature rising process, not only the power supply device 1 combining the lithium ion battery and the lead battery, but also the power source combining the first battery B1 as the lithium ion assembled battery and the second battery B2 as the lithium ion assembled battery. The apparatus 1 can also be used as a power source for the vehicle to achieve low temperature startability, and provide a light power source for the vehicle. In addition, there is a system in which a power source in which a capacitor is connected in parallel with a lead battery is used as a power source device 1 as a power source for a vehicle. When it is going to secure the amount of electric power, it has been a problem to invite an increase in the size of the power source, but by using both the first battery B1 and the second battery B2 as a lithium ion assembled battery, and performing the temperature increase process, It becomes possible to solve the problem of the power source using the capacitor.

  Furthermore, when charging from the second battery B2 to the first battery B1 at a low temperature, generally, the charging of the lithium ion battery at a low temperature often limits the current value. For example, in the case of a lithium ion battery using a carbon-based material for the negative electrode, charging with a large current increases the possibility that Li will precipitate on the negative electrode and cause an internal short circuit in the battery. Limited use. In the present embodiment, a battery using lithium titanate (LTO) as a negative electrode is used as the first battery B1, and the LTO has a potential of 1.5 V with respect to the Li deposition potential as a material. A charging current can be passed, and the battery can be safely heated by repeated charging and discharging.

(Second Embodiment)
The present embodiment is an example in which a plurality of discharge loads are connected to the first battery. In the following description, description of the same parts as those in the first embodiment is omitted.

  FIG. 7 is a diagram illustrating an example of a configuration of a power supply system according to the second embodiment. As shown in FIG. 7, the power supply apparatus 700 of the power supply system according to the present embodiment includes a control unit 101, a first battery B1, a second battery B2, a temperature sensor 103, a second switch SW2, and a third switch SW3. The plurality of discharge loads 102a and 102b connected in parallel and the first switches SW1a and SW1b provided in the discharge loads 102a and 102b, respectively.

  In the present embodiment, when executing the temperature raising process, the control unit 101 turns on the plurality of first switches SW1a and SW1b to switch the plurality of discharge loads 102 connected in parallel and the first battery B1. The electric power stored in the first battery B1 is discharged to the plurality of discharge loads 102a and 102b connected in parallel. Thereby, compared with the case where the electric power stored in the first battery B1 is discharged to one discharge load 102, the resistance in the parallel state of the discharge loads 102a and 102b is reduced, and the first battery B1 Since the total discharge current flowing increases and the temperature rise of the first battery B1 can be accelerated, the performance as a power source for starting the vehicle can be improved.

  When the ratio between the internal resistance of the first battery B1 at the cryogenic temperature and the resistance of the discharge load 102 is in the range of 2: 1 to 1:10, the current to the discharge loads 102a and 102b is efficiently transferred to the first battery B1. Therefore, it is preferable to prepare a plurality of discharge loads 102a and 102b or connect the discharge loads 102a and 102b in parallel. As described above, by using the discharge loads 102a and 102b as heaters for heating the first battery B1, or by using a part of the discharge loads 102a and 102b as heaters, the first battery B1 can be more efficiently used. The temperature can be raised.

  In addition, the control unit 101 increases the number of parallel connections of the discharge loads 102a and 102b that discharge from the first battery B1 as the temperature of the first battery B1 detected by the temperature sensor 103 increases, so that the discharge loads 102a and 102b are increased. It is also possible to efficiently draw a current from the first battery B1 by reducing the resistance of 102b.

  For example, when the temperature T of the first battery B1 detected by the temperature sensor 103 is −30 ° C., the control unit 101 switches on only one of the two first switches SW1 (for example, the first switch SW1a). The power stored in the first battery B1 is discharged only to one discharge load 102a. In addition, when the temperature T of the first battery B1 detected by the temperature sensor 103 reaches −20 ° C., the control unit 101 switches both of the two first switches SW1a and SW1b on, The electric power stored in the first battery B1 is discharged to the discharge loads 102a and 102b. Thereby, the current flowing from the first battery B1 to the discharge load 102 increases, and the temperature of the first battery B1 can be raised. Since the battery voltage of the first battery B1 decreases to the predetermined voltage V1 in a shorter time, the cycle in which the temperature raising process is repeated becomes shorter, but the temperature of the first battery B1 can be increased in a shorter time.

  Thus, according to the power supply system concerning 2nd Embodiment, the cold start of a vehicle can be implement | achieved in a short time, and the performance as a power supply for start-up can be improved.

  As described above, according to the first and second embodiments, the lithium ion battery can be used as a power source for starting a vehicle even at an extremely low temperature.

DESCRIPTION OF SYMBOLS 1,700 Power supply device 101 Control part 102 Discharge load 103 Temperature sensor B1 1st battery B2 2nd battery SW1 1st switch SW2 2nd switch SW3 3rd switch D Generator E Engine H Auxiliary machine S Starter

Claims (9)

A first battery having a lithium ion battery capable of supplying power to the first load;
A discharge load connected to the first battery and discharging the electric power stored in the first battery;
A first switch capable of switching between connection and disconnection of the discharge load and the first battery;
A second battery connected in parallel with the first battery;
A second switch capable of switching between parallel connection and disconnection of the first battery and the second battery;
A measurement unit for measuring the temperature of the first battery;
Control for supplying power from at least the first battery to the first load when the first process is executed until the temperature of the first battery reaches the predetermined temperature and the temperature of the first battery reaches the predetermined temperature. And comprising
The first process switches the first switch to connect the first battery and the discharge load to discharge the electric power stored in the first battery, and the battery voltage of the first battery is first. When the voltage drops below a predetermined voltage, the first switch is switched to disconnect the first battery and the discharge load, and then the second switch is switched to connect the first battery and the second battery in parallel. Then, power is supplied from the second battery to the first battery, and the first battery is charged until the battery voltage of the first battery reaches a second predetermined voltage higher than the first predetermined voltage.   In the first process, after the battery voltage of the first battery reaches the second predetermined voltage, the second switch is switched to disconnect the first battery from the second battery. 2. The power supply device according to claim 1, wherein the discharge of the electric power stored in the first battery and the charging of the first battery are repeated until the temperature of the battery reaches the predetermined temperature.   The power supply device according to claim 1, comprising a plurality of the discharge loads connected in parallel.   When the temperature of the first battery reaches the predetermined temperature, the control unit switches the second switch to connect the first battery and the second battery in parallel, so that the first battery and the first battery The power supply device according to claim 1, wherein power is supplied from both of the two batteries to the first load.   2. The power supply device according to claim 1, wherein the discharge load is a heater capable of heating the first battery by generating heat by the electric power discharged from the first battery.   The power supply device according to claim 1, wherein the second battery is a battery having a larger capacity than the first battery.   The power supply device according to claim 1, wherein the first load is a starter that starts an engine of a vehicle.   The power supply device according to claim 1, wherein the second battery is an assembled battery made of a lead battery or a lithium ion battery.   The power supply device according to claim 1, wherein the first battery includes a lithium ion battery having lithium titanate as a negative electrode.

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