Power storage device and method for estimating remaining power of battery of the same

Abstract

To precisely estimate the remaining power of a battery.SOLUTION: A storage device having a nickel hydrogen battery includes: a recording unit for recording the remaining power of a battery estimated on the basis of charge-discharge currents of a nickel hydrogen battery as a first remaining power when the power storage device is stopped; an estimation unit for determining the remaining power of the battery estimated on the basis of the battery voltage of the nickel hydrogen battery as a second remaining power when the power storage device is activated after being stopped; and a determination unit for determining which of the first remaining power and the second remaining power is to be employed as the remaining power of the battery of the nickel hydrogen battery when the battery is activated, according to the operation state of the power storage device when the device is stopped.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a power storage device and a method for estimating the remaining battery capacity of the power storage device.

Background Art

[0002] As a method for estimating the remaining battery capacity of a nickel-hydrogen battery, a method of measuring the battery voltage and estimating the remaining battery capacity based on the battery voltage is mainly used. For example, Patent Document 1 shows that the remaining capacity of a secondary battery is estimated by measuring the voltage time average value of the secondary battery and using the voltage time average value or the like.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, due to its characteristics, a nickel-hydrogen battery has a phenomenon in which the battery voltage varies greatly depending on whether it is not being charged or discharged, being charged, or being discharged. Therefore, with a nickel-hydrogen battery, it has not been possible to accurately estimate the remaining battery capacity by the above-described method.

[0005] An object of the present invention is to provide a power storage device and a method for estimating the remaining battery capacity of the power storage device that can accurately estimate the remaining battery capacity.

Means for Solving the Problems

[0006] The power storage device according to the present invention is in a power storage device having a nickel-hydrogen battery, a recording unit that records, as a first remaining capacity, the remaining battery capacity estimated based on the charge and discharge current of the nickel-hydrogen battery when the power storage device stops; After the stop, when the power storage device is started, an estimation unit that obtains, as a second remaining amount, the remaining battery amount estimated based on the battery voltage of the nickel-metal hydride battery; A determination unit that determines which of the first remaining amount and the second remaining amount to adopt according to the operating state of the power storage device at the time of the stop, as the remaining battery amount of the nickel-metal hydride battery at the time of the start.

[0007] The method for estimating the remaining battery amount of the power storage device according to the present invention is as follows: In a method for estimating the remaining battery amount of a power storage device having a nickel-metal hydride battery, The remaining battery amount estimated based on the charge and discharge current of the nickel-metal hydride battery is recorded as a first remaining amount when the power storage device stops. After the stop, when the power storage device is started, the remaining battery amount estimated based on the battery voltage of the nickel-metal hydride battery is obtained as a second remaining amount. As the remaining battery amount of the nickel-metal hydride battery at the time of the start, it is determined which of the first remaining amount and the second remaining amount to adopt according to the operating state of the power storage device at the time of the stop.

Advantages of the Invention

[0008] According to the present invention, the remaining battery amount can be accurately estimated.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0010] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0011] [Power Storage Device] FIG. 1 is a diagram showing a power storage device 10 which is an example of a power storage device according to the present embodiment.

[0012] The power storage device 10 is connected between the power supply 100 and the load 200 by the power supply lines Wp1 and Wn1. When power is supplied from the power supply 100 through the power supply lines Wp1 and Wn1, power is supplied to the load 200 and also to the power storage device 10, and the power storage device 10 charges the battery pack 11 described later. On the other hand, for example, when power is not supplied from the power supply 100 due to a power outage or the like, the power storage device 10 discharges the battery pack 11 and supplies the power stored in the battery pack 11 to the load 200 through the power supply lines Wp1 and Wn1. By such an operation, the power storage device 10 can operate as an uninterruptible power supply device.

[0013] In the present embodiment, the power supply 100 is a DC power supply, and for example, it converts commercial AC power into DC power and supplies it to the power storage device 10 and the load 200. Also, the load 200 is a device that operates with the DC power supplied from the power supply 100 or the power storage device 10.

[0014] The power storage device 10 includes a battery pack 11, a regulator 12, a charge / discharge current measurement unit 13, a microcomputer 14, a charge switch S1, a discharge switch S2, and the like.

[0015] Also, the power storage device 10 has signal lines 21 to 24 as signal lines for measuring the state inside the power storage device 10, and has power supply lines Wp1 to Wp6 and Wn1 to Wn3 as power supply lines for power supply.

[0016] The battery pack 11 has a nickel - hydrogen battery 111, a battery temperature measurement unit 112, and the like. In the present embodiment, the battery pack 11 has a plurality of nickel - hydrogen batteries 111, and as an example, it consists of five nickel - hydrogen batteries 111 connected in series. Note that in the battery pack 11, the number of nickel - hydrogen batteries 111 and the connection configuration (series connection, parallel connection, etc.) of the nickel - hydrogen batteries 111 can be changed as appropriate.

[0017] The battery temperature measuring unit 112 measures the battery temperature of the nickel-metal hydride battery 111. The battery temperature measured by the battery temperature measuring unit 112 is input to the microcomputer 14 via the signal line 23. The microcomputer 14 acquires the battery temperature input from the signal line 23. Any device can be used as the battery temperature measuring unit 112 as long as it can measure the battery temperature of the nickel-metal hydride battery 111 and input it to the microcomputer 14.

[0018] Regulator 12 is a device that converts (boosts or reduces) DC power supplied from power source 100 or battery pack 11 to a constant voltage suitable for microcomputer 14. The voltage of the DC power supplied from battery pack 11 gradually decreases as it is discharged, but regulator 12 can supply a constant voltage to microcomputer 14.

[0019] The charge / discharge current measuring unit 13 is provided on the power line Wn2 that connects between the negative electrode of the battery pack 11 and the power line Wn1, and measures the current that flows when the battery pack 11 is charged or discharged. For example, the charge / discharge current measuring unit 13 measures the current that flows through the power line Wn2 by measuring the potential difference across a resistor 131 that the charge / discharge current measuring unit 13 has. The charge / discharge current measured by the charge / discharge current measuring unit 13 is input to the microcomputer 14 via a signal line 24. The microcomputer 14 acquires the charge / discharge current input from the signal line 24. Any charge / discharge current measuring unit 13 can be used as long as it can measure the current that flows when the battery pack 11 is charged or discharged and input it to the microcomputer 14.

[0020] The charging switch S1 is provided on the power line Wp2 and is controlled to be in an on state by the microcomputer 14 during charging of the battery pack 11 and in an off state during discharging from the battery pack 11. Also, the discharging switch S2 is provided on the power line Wp3 and is controlled to be in an on state by the microcomputer 14 during discharging from the battery pack 11 and in an off state during charging of the battery pack 11. Further, when stopping (shutting down) the power storage device 10, the charging switch S1 and the discharging switch S2 are controlled to be in an off state by the microcomputer 14. As the charging switch S1 and the discharging switch S2, for example, a power MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor), a contactor (electromagnetic contactor), or the like can be used.

[0021] The microcomputer 14 is connected to the regulator 12 via the power line Wp4, connected to the power line Wn1 via the power line Wn3, and operates with the power supplied from the regulator 12.

[0022] The microcomputer 14 has input terminals to which the signal lines 21 and 22 are connected, in addition to the input terminals to which the above-described signal lines 23 and 24 are connected. The signal line 21 is connected to the power line Wp4 connected to the output side of the power supply 100, and the input voltage of the power input from the power supply 100 is input to the microcomputer 14. The microcomputer 14 measures and acquires the voltage input from the signal line 21 as the input voltage.

[0023] The signal line 22 is connected to the power line Wp5 connected to the positive electrode of the battery pack 11, and the battery voltage of the battery pack 11 is input to the microcomputer 14. The microcomputer 14 measures and acquires the voltage input from the signal line 22 as the battery voltage.

[0024] The microcomputer 14 also has an output terminal to which a signal line (not shown) for controlling the charging switch S1 and the discharging switch S2 is connected. The microcomputer 14 measures the input voltage from the power supply 100 via the signal line 21, and when there is an input voltage from the power supply 100, turns on the charging switch S1 (the discharging switch S2 is in the off state) to charge the battery pack 11. On the other hand, when there is no input voltage from the power supply 100, the discharging switch S2 is turned on (the charging switch S1 is in the off state), the battery pack 11 is discharged, and the power stored in the battery pack 11 is supplied to the load 200 via the power lines Wp1 and Wn1.

[0025] Also, when the microcomputer 14 stops (shuts down) the power storage device 10, it turns off the charging switch S1 and the discharging switch S2.

[0026] The microcomputer 14 is composed of a known microcomputer control device. In the present embodiment, the microcomputer 14 functionally includes a recording unit 141, an estimation unit 142, a determination unit 143, and the like.

[0027] The recording unit 141 records information regarding the power storage device 10. In the present embodiment, the recording unit 141 records the operating state (charging state, discharging state, standby state) of the power storage device 10, the measured values measured via the signal lines 21 to 24, the remaining battery level estimated by the estimation unit 142, and the like. As the recording unit 141, a non-volatile memory, for example, an EEPROM (Erasable Programmable Read Only Memory) or the like can be used. Note that the standby state is a state that is neither the charging state nor the discharging state.

[0028] In the present embodiment, as will be described later, the recording unit 141 records the operating state of the power storage device 10 when it stops. However, if the microcomputer 14 can determine the operating state of the power storage device 10 when it stops, the recording unit 141 does not necessarily have to record the operating state of the power storage device 10. For example, the microcomputer 14 may determine the operating state of the power storage device 10 when it stops based on a flag corresponding to the operating state of the power storage device 10.

[0029] The estimation unit 142 estimates the remaining battery level of the battery pack 11 based on the battery voltage of the battery pack 11 acquired via the signal line 22. Further, after the battery pack 11 is fully charged, the estimation unit 142 estimates the remaining battery level of the battery pack 11 based on the charge and discharge current of the battery pack 11 acquired via the signal line 24. Note that for the estimation of the remaining battery level based on the battery voltage and the estimation of the remaining battery level based on the charge and discharge current, known methods may be used, and detailed descriptions are omitted here.

[0030] The determination unit 143 determines which of the recorded remaining amount and the estimated remaining amount (the first remaining amount and the second remaining amount in the present invention) described later is to be adopted according to the operating state at the time of stopping the power storage device 10 as the remaining battery level of the battery pack 11 at the time of starting the power storage device 10. Here, the recorded remaining amount is the remaining battery level estimated by the estimation unit 142 based on the charge and discharge current of the battery pack 11 after the battery pack 11 is fully charged and recorded by the recording unit 141 at the time of stopping the power storage device 10. The estimated remaining amount is the remaining battery level estimated by the estimation unit 142 based on the battery voltage of the battery pack 11 at the time of starting the power storage device 10 after the power storage device 10 is stopped. Note that the operations of the recording unit 141, the estimation unit 142, and the determination unit 143 in the microcomputer 14 will be described in more detail with reference to the flowchart of FIG. 2 described later.

[0031] The microcomputer 14 uses the signal lines 21 to 24 to acquire information necessary for controlling the power storage device 10, and based on the acquired information, controls the charge and discharge of the battery pack 11 or estimates the remaining battery level of the battery pack 11.

[0032] The power supply lines Wp1 and Wn1 connect the power supply 100 and the load 200 via the power storage device 10. A diode D1 is provided on the power supply line Wp1. The diode D1 is arranged such that the direction in which current flows during power supply from the power supply 100 is the forward direction. Further, the diode D1 is arranged between the power supply line Wp2 and the power supply line Wp3 respectively connected to the power supply line Wp1 so that current does not flow to the power supply 100 side when the power stored in the battery pack 11 is supplied to the load 200.

[0033] The power line Wp2 connects the power line Wp1 and the charging switch S1. The power line Wp2 is connected to the power line Wp1 on the power supply 100 side from the diode D1 and is the power line used for charging the battery pack 11. A diode D2 is provided on the power line Wp2. The diode D2 is arranged such that the direction in which current flows during charging is the forward direction.

[0034] The power line Wp3 connects the power line Wp1 and the discharging switch S2. The power line Wp3 is connected to the power line Wp1 on the load 200 side from the diode D1 and is the power line used for discharging the battery pack 11. A diode D3 is provided on the power line Wp3. The diode D3 is arranged such that the direction in which current flows during discharging is the forward direction.

[0035] The power line Wp4 connects the power line Wp1 and the microcontroller 14. The power line Wp4 is connected to the power line Wp1 on the power supply 100 side from the diode D1 and is the power line used for supplying power to the microcontroller 14. A diode D4 and a regulator 12 are provided on the power line Wp4. The diode D4 is arranged such that the direction in which current flows during power supply from the power supply 100 is the forward direction. Also, the diode D4 is arranged such that no current flows to the power supply 100 side when supplying the power stored in the battery pack 11 to the microcontroller 14. In the power line Wp4, the regulator 12 is arranged on the microcontroller 14 side from the diode D4.

[0036] The power line Wp5 connects the charging switch S1 and the discharging switch S2 to the positive electrode of the battery pack 11.

[0037] The power line Wp6 connects the power line Wp4 and the power line Wp5. The power line Wp6 is connected between the diode D4 and the regulator 12 in the power line Wp4. A diode D5 is provided on the power line Wp6. The diode D5 is arranged such that the direction in which current flows during power supply from the battery pack 11 is the forward direction. Also, the diode D5 is arranged such that no current flows to the battery pack 11 side when power is supplied from the power supply 100 to the microcomputer 14.

[0038] The power line Wn2 connects the negative electrode of the battery pack 11 and the power line Wn1 via the charge / discharge current measurement unit 13. The power line Wn3 connects the microcomputer 14 and the power line Wn1.

[0039] The power storage device 10 controls the charging and discharging of the battery pack 11 and estimates the remaining battery level of the battery pack 11 (normal processing) according to the above-described configuration.

[0040] Note that the power storage device 10 may include a display device. In this case, for example, the microcomputer 14 displays the estimated remaining battery level on the display device and presents it to the user.

[0041] [Method for Estimating Remaining Battery Level of Power Storage Device] FIG. 2 is a flowchart for explaining the method for estimating the remaining battery level in the power storage device 10.

[0042] First, as a premise, when the power storage device 10 stops (immediately before stopping), the microcomputer 14 records the operating state (charging state, discharging state, standby state) of the power storage device 10 immediately before stopping in the recording unit 141. Also, the microcomputer 14 records the remaining battery level of the battery pack 11 immediately before stopping as the recorded remaining level in the recording unit 141. The remaining battery level that becomes the recorded remaining level is the remaining battery level estimated based on the charge / discharge current of the battery pack 11 after the battery pack 11 is fully charged, as described above. Therefore, when the power storage device 10 stops without the battery pack 11 being fully charged, the recording unit 141 does not record the recorded remaining level.

[0043] (Step S11) When the power storage device 10 is activated, the microcomputer 14 acquires the battery voltage of the battery pack 11 using the signal line 22. Note that the microcomputer 14 may acquire the battery temperature of the battery pack 11 using the signal line 23 as necessary.

[0044] (Step S12) In the estimator 142, the microcomputer 14 estimates the remaining battery level based on the battery voltage of the battery pack 11. The remaining battery level estimated here is referred to as the estimated remaining level.

[0045] Then, in the determination unit 143, the microcomputer 14 makes determinations in steps S13 to S23 described below according to the operating state at the time of stopping the power storage device 10.

[0046] (Step S13) The microcomputer 14 checks whether the acquired battery voltage is greater than a predetermined voltage and whether it was fully charged at the time of the previous stop. If the acquired battery voltage is greater than the predetermined voltage and it was fully charged at the time of the previous stop (YES), the process proceeds to step S14. If the acquired battery voltage is less than or equal to the predetermined voltage or it was not fully charged at the time of the previous stop (NO), the process proceeds to step S15.

[0047] The predetermined voltage is changed according to the configuration of the nickel-metal hydride battery 111 in the battery pack 11. Here, as an example (see FIG. 1), since the battery pack 11 is composed of five nickel-metal hydride batteries 111 connected in series, it is set to 55V.

[0048] Also, full charge does not necessarily mean a charge rate of 100%. Here, as an example, when charging is started and the charge rate is 92% or more, the microcomputer 14 determines that it is fully charged.

[0049] Therefore, here, as an example, it is checked whether the acquired battery voltage is greater than 55V and whether the charge rate was 92% or more at the time of the previous stop. If the acquired battery voltage is greater than 55V and the charge rate was 92% or more at the time of the previous stop (YES), the process proceeds to step S14. If the acquired battery voltage is 55V or less, or the charge rate was less than 92% at the time of the previous stop (NO), the process proceeds to step S15.

[0050] (Step S14) When the acquired battery voltage is greater than a predetermined voltage and the battery pack was fully charged at the time of the previous stop (YES in step S13), the microcomputer 14 determines that the battery pack 11 is in a fully charged state and proceeds to the normal processing of the power storage device 10.

[0051] (Step S15) The microcomputer 14 checks whether there is no remaining recorded amount or whether it was in a standby state at the time of the previous stop. The microcomputer 14 checks the remaining recorded amount recorded in the recording unit 141 and the operating state of the power storage device 10 at the time of the previous stop to check whether there is a remaining recorded amount and whether it was in a standby state at the time of the previous stop. If there is no remaining recorded amount or it was in a standby state at the time of the previous stop (YES), the process proceeds to step S16. If there is a remaining recorded amount and it was not in a standby state at the time of the previous stop (NO), the process proceeds to step S17.

[0052] (Step S16) When there is no remaining recorded amount or it was in a standby state at the time of the previous stop (YES in step S15), the microcomputer 14 adopts the estimated remaining amount estimated in step S12 as the remaining battery amount of the battery pack 11 and proceeds to the normal processing of the power storage device 10.

[0053] (Step S17) The microcomputer 14 checks whether it was in a charged state at the time of the previous stop. The microcomputer 14 checks the operating state of the power storage device 10 recorded in the recording unit 141 at the time of the previous stop to check whether it was in a charged state at the time of the previous stop. If it was in a charged state at the time of the previous stop (YES), it proceeds to step S18. If it was not in a charged state at the time of the previous stop (NO), that is, if it was in a discharged state at the time of the previous stop, it proceeds to step S21.

[0054] (Step S18) The microcomputer 14 checks whether the estimated remaining amount is greater than the recorded remaining amount. That is, it checks whether the estimated remaining amount estimated in step S12 is greater than the recorded remaining amount recorded in the recording unit 141. If the estimated remaining amount is greater than the recorded remaining amount (YES), it proceeds to step S19. If the estimated remaining amount is less than or equal to the recorded remaining amount (NO), it proceeds to step S20.

[0055] (Step S19) When the estimated remaining amount is greater than the recorded remaining amount (YES in step S18), the microcomputer 14 adopts the recorded remaining amount recorded in the recording unit 141 as the battery remaining amount of the battery pack 11 and shifts to the normal processing of the power storage device 10.

[0056] (Step S20) When the estimated remaining amount is less than or equal to the recorded remaining amount (NO in step S18), the microcomputer 14 adopts the estimated remaining amount estimated in step S12 as the battery remaining amount of the battery pack 11 and shifts to the normal processing of the power storage device 10.

[0057] That is, when it was in a charged state at the time of the previous stop, the battery voltage becomes higher than when there has been no charge or discharge. Therefore, the determination unit 143 adopts the lower of the estimated remaining amount and the recorded remaining amount as the battery remaining amount of the battery pack 11 when starting the power storage device 10.

[0058] (Step S21) The microcomputer 14 checks whether the estimated remaining amount is greater than the recorded remaining amount. That is, it checks whether the estimated remaining amount estimated in step S12 is greater than the recorded remaining amount recorded in the recording unit 141. If the estimated remaining amount is greater than the recorded remaining amount (YES), it proceeds to step S22; if the estimated remaining amount is less than or equal to the recorded remaining amount (NO), it proceeds to step S23.

[0059] (Step S22) When the estimated remaining amount is greater than the recorded remaining amount (YES in step S21), the microcomputer 14 adopts the estimated remaining amount estimated in step S12 as the battery remaining amount of the battery pack 11 and proceeds to the normal processing of the power storage device 10.

[0060] (Step S23) When the estimated remaining amount is less than or equal to the recorded remaining amount (NO in step S21), the microcomputer 14 adopts the recorded remaining amount recorded in the recording unit 141 as the battery remaining amount of the battery pack 11 and proceeds to the normal processing of the power storage device 10.

[0061] That is, when it was in a discharged state at the time of the previous stop, since the battery voltage becomes lower than when no charge / discharge was performed, the determination unit 143 adopts the higher value of the estimated remaining amount and the recorded remaining amount as the battery remaining amount of the battery pack 11 when starting the power storage device 10.

[0062] Conventionally, the battery voltage has been used to estimate the battery remaining amount of a nickel-metal hydride battery. However, as described above, when no charge / discharge is performed, when charging is performed, and when discharging is performed, the battery voltage varies significantly. For example, when charging is performed, the battery voltage becomes higher than when no charge / discharge is performed, and when discharging is performed, the battery voltage becomes lower than when no charge / discharge is performed. Therefore, especially when starting the power storage device, if the battery remaining amount is not estimated according to the operating state of the power storage device at the time of the previous stop, the estimated battery remaining amount will deviate significantly, and it is difficult to accurately estimate the battery remaining amount.

[0063] Therefore, in the present embodiment, as described above, the microcomputer 14 records, in the recording unit 141, the remaining battery level estimated based on the charge and discharge current of the battery pack 11 as the recorded remaining level when the power storage device 10 stops. Further, the microcomputer 14 obtains, in the estimation unit 142, the remaining battery level estimated based on the battery voltage of the battery pack 11 as the estimated remaining level when the power storage device 10 starts up after the power storage device 10 stops. Then, the microcomputer 14 determines, in the determination unit 143, which of the estimated remaining level and the recorded remaining level to adopt as the remaining battery level of the battery pack 11 when the power storage device 10 starts up, according to the operating state when the power storage device 10 stops.

[0064] According to the present embodiment configured as described above, the power storage device 10 (microcomputer 14) estimates the remaining battery level of the battery pack 11 when the power storage device 10 starts up, according to the operating state (charging state, discharging state, standby state) when the power storage device 10 stopped last time. Thereby, the power storage device 10 (microcomputer 14) estimates the remaining battery level of the battery pack 11 in consideration of the operating state when the power storage device 10 stopped last time, and can accurately estimate the remaining battery level.

[0065] The embodiments of the present invention have been described above. Note that the above description is an illustration of a preferred embodiment of the present invention, and the scope of the present invention is not limited thereto. That is, the description of the configuration of the above device and the shape of each part is an example, and it is obvious that various changes and additions to these examples are possible within the scope of the present invention.

Industrial Applicability

[0066] The present invention is useful as a power storage device having a nickel-metal hydride battery.

Explanation of Reference Numerals

[0067] 10 Power storage device 11 Battery pack 12 Regulator 13 Charge and discharge current measurement unit 14 Microcomputer 21~24 Signal lines 100 Power supply 111 Nickel-metal hydride battery 112 Battery temperature measurement unit 131 Resistor 141 Recording unit 142 Estimation unit 143 Judgment unit 200 Load S1 Charge switch S2 Discharge switch Wp1~Wp6, Wn1~Wn3 Power supply lines

Claims

1. In a power storage device having a nickel-hydrogen battery, a recording unit that records, as a first remaining amount, the remaining battery amount estimated based on the charge and discharge current of the nickel-hydrogen battery when the power storage device stops; an estimation unit that, when the power storage device starts up after the stop, obtains, as a second remaining amount, the remaining battery amount estimated based on the battery voltage of the nickel-hydrogen battery; a determination unit that determines which of the first remaining amount and the second remaining amount to adopt as the remaining battery amount of the nickel-hydrogen battery at the time of startup according to the operating state of the power storage device at the time of stop; A power storage device.

2. The operating state includes a charging state, a discharging state, and a standby state other than the charging state and the discharging state. The power storage device according to Claim 1.

3. When the operating state is the standby state, the determination unit adopts the second remaining amount as the remaining battery amount of the nickel-hydrogen battery at the time of startup. The power storage device according to Claim 2.

4. When the operating state is the charging state, if the second remaining amount is greater than the first remaining amount, the determination unit adopts the first remaining amount as the remaining battery amount of the nickel-hydrogen battery at the time of startup; if the second remaining amount is less than or equal to the first remaining amount, the determination unit adopts the second remaining amount. The power storage device according to Claim 2.

5. When the operating state is the discharging state, if the second remaining amount is greater than the first remaining amount, the determination unit adopts the second remaining amount as the remaining battery amount of the nickel-hydrogen battery at the time of startup; if the second remaining amount is less than or equal to the first remaining amount, the determination unit adopts the first remaining amount. The power storage device according to Claim 2.

6. The recording unit records the operating state of the power storage device at the time of stop. The power storage device according to Claim 2.

7. In a method for estimating the remaining battery amount of a power storage device having a nickel-hydrogen battery, recording, as a first remaining amount, the remaining battery amount estimated based on the charge and discharge current of the nickel-hydrogen battery when the power storage device stops; after the stop, when the power storage device starts up, obtaining, as a second remaining amount, the remaining battery amount estimated based on the battery voltage of the nickel-hydrogen battery; determining which of the first remaining amount and the second remaining amount to adopt as the remaining battery amount of the nickel-hydrogen battery at the time of startup according to the operating state of the power storage device at the time of stop. A method for estimating the remaining battery amount of a power storage device.

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