Battery deterioration management system

Abstract

The purpose of the present invention is to provide a technique with which it is possible to appropriately select an economically effective measure and an implementation time of the measure as a measure to be implemented when a secondary battery is deteriorated. This battery deterioration management system calculates, on the basis of cost data in which costs accompanying the implementation of measures for reducing the deterioration state of a battery are described, the costs required to implement said measures, and determines, on the basis of said costs, an economically effective measure and the implementation time of said measure (referring to Figure 4).

Description

Technical Field

[0001] The present invention relates to a technology for managing the degree of battery degradation. Background Art

[0002] Secondary batteries gradually deteriorate with use. Once degradation reaches a certain level, some measures must be taken. Examples of these measures include (a) rebalancing to equalize the charge state of each battery cell, (b) regenerating severely degraded batteries (rebuilding them as recycled parts), and (c) converting them to other uses.

[0003] Patent document 1 discloses "providing a system capable of suppressing the transportation cost of used secondary batteries and selling used secondary batteries inexpensively" as a subject, and records that "the used secondary battery recycling system of the present invention assists in the recycling of used secondary batteries used as secondary batteries for driving vehicles. It is equipped with: a purchase request information receiving unit that receives purchase request information of used secondary batteries; a trade-in request information receiving unit that receives trade-in request information including information indicating the deterioration state of secondary batteries mounted on vehicles; an extraction unit that extracts purchase request information whose use of used secondary batteries is consistent with the deterioration state included in the trade-in request information; a sales price determination unit that determines the sales price of the secondary batteries to be traded in; a transportation cost estimation unit that estimates the transportation cost from each trade-in facility of the secondary batteries to be traded in to the delivery location; and a trade-in price determination unit that determines the trade-in price in each trade-in facility based on the sales price and transportation cost of the secondary batteries to be traded in" such technology (see abstract).

[0004] Patent Document 2, a technology related to the present invention, describes a method for calculating the battery capacity of a battery pack. This application describes a method for diagnosing a battery pack using a system that obtains detection data of the current and temperature of a battery pack having a structure in which a plurality of battery cells are connected in series, as well as the voltage of each battery cell. The method includes: using the current and temperature, the voltage of each battery cell, an SOC function of OCV, and a resistance table to calculate the charge capacity and SOC of each battery cell, and calculating the imbalance value and resistance, which are estimated values ​​of the SOC of each battery cell when the battery pack is fully charged; and calculating the energy capacity of the battery pack using the charge capacity, imbalance value, and resistance. Thus, the energy capacity of the battery pack can be accurately calculated even in an unbalanced state" (see abstract).

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Laid-Open No. 2021-124982

[0008] Patent Document 2: WO2022 / 024885A1 Summary of the Invention

[0009] Problems to be solved by the invention

[0010] The purpose of the prior art such as Patent Document 1 is to suppress the costs associated with the reuse of used batteries. However, the costs incurred when reusing degraded secondary batteries also include costs that vary over time, so it is preferable to consider such dynamically varying costs. In addition, when determining what measures should be implemented, it is preferable to consider the impact of the costs that vary over time and select measures with high economic effects and the time when such measures are implemented. The same applies to the implementation of measures other than recycling. In the prior art, since such costs that vary over time are not fully considered, it is possible to implement measures that may not be economically effective, or to implement measures at a time when the economic effects may not be high.

[0011] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a technique capable of appropriately selecting a measure with high economical effect and a timing for implementing the measure as a measure to be implemented when a secondary battery deteriorates.

[0012] Means for solving problems

[0013] The battery degradation management system of the present invention calculates the cost required to implement measures to reduce the degradation state of the battery based on cost data that records the costs associated with implementing the measures, and based on the costs, determines the economically most effective measures and the implementation time of the measures.

[0014] Effects of the Invention

[0015] The battery degradation management system of the present invention can appropriately select economically effective measures and the timing for implementing the measures as measures to be implemented when a secondary battery degrades. Other problems, structures, and effects of the present invention will become apparent from the following description of the embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a configuration diagram of the battery deterioration degree management system 1 according to the first embodiment.

[0017] Figure 2 It is a schematic diagram showing the flow of processing performed by the calculation unit 11.

[0018] Figure 3 The results of predicting the temporal change of the SOH of the battery cell are shown.

[0019] Figure 4 It is a schematic diagram showing the flow of processing performed by the calculation unit 11.

[0020] Figure 5 This is a diagram showing the results of measuring the SOH of each battery cell. DETAILED DESCRIPTION

[0021] <Implementation Method 1>

[0022] Figure 1 This is a block diagram of a battery degradation management system 1 according to Embodiment 1 of the present invention. The battery degradation management system 1 manages the state of health (SOH) of secondary batteries (hereinafter referred to as batteries). The battery degradation management system 1 includes a calculation unit 11 and a storage unit 12 .

[0023] The calculation unit 11 receives characteristic data and measurement data and uses them to estimate the battery's state of health (SOH). Any known technique can be used as the estimation step. Based on the estimated SOH, the calculation unit 11 also identifies batteries experiencing progressive degradation and determines measures to be taken for those batteries. When determining measures, the unit seeks to optimize the economic benefits of the measures. Specific examples of measures and the determination process are described later. The storage unit 12 stores data used by the calculation unit 11.

[0024] Characteristic data is data that describes the physical characteristics of the battery and can be obtained in advance before estimating the SOH. The characteristic data describes the SOC-OCV curve, SOC-charge resistance curve, SOC-discharge resistance curve, number of battery cells, rated capacity (Wh), etc. The SOC-OCV curve describes the relationship between the battery's SOC (State Of Charge) and OCV (Open Circuit Voltage). The SOC-charge resistance curve describes the relationship between the battery's SOC and charge resistance. The SOC-discharge resistance curve describes the relationship between the battery's SOC and discharge resistance. The number of battery cells is the number of battery cells that make up the battery. The rated capacity (Wh) is the rated capacity of the battery.

[0025] Measurement data describes the results of measuring the physical state of a battery and can be obtained, for example, from a battery management unit (BMU). Measurement data includes a timestamp, battery current, battery voltage, and battery temperature. The timestamp indicates the date and time the measurement data was acquired (or the date and time the measurement was performed). The battery current, battery voltage, and battery temperature are the battery's output current, battery output voltage, and battery temperature (or the temperature of the battery's surrounding environment), respectively.

[0026] Figure 2It is a schematic diagram showing the processing flow implemented by the operation unit 11. The operation unit 11 uses the characteristic data and the measurement data to estimate the SOH of the battery. Specifically, the battery capacity can be calculated using the cumulative value of the current value during charging and the SOC of the battery at the start and end of charging. Moreover, the SOH can be estimated based on "SOH = 100 × battery capacity / rated capacity of the battery". Alternatively, any known technology such as Patent Document 2 can be used. As another method, for example, the time change of the battery voltage during the rest period after the charging action or the discharging action can be obtained, and the SOH can be estimated based on the correspondence between the time change and the SOH.

[0027] The calculation unit 11 predicts the temporal variation of the SOH. Since the SOH gradually decreases over time, for example, the temporal variation of the SOH in the future can be predicted based on the temporal rate of decrease. Prediction can also be performed using any other method. The prediction of the temporal variation of the future SOH can be performed using linear approximation, ARMA (autoregressive moving average) or Weibull distribution, or any other method.

[0028] The calculation unit 11 identifies batteries with reduced SOH and determines measures to be taken for these batteries. Examples of measures include (a) rebalancing to equalize the charge states of the batteries constituting the battery pack, (b) rebuilding (regenerating) severely degraded batteries (rebuilding them as recycled products), and (c) converting them to other uses.

[0029] For example, a battery cell experiencing advanced deterioration will experience a greater decrease in SOC during discharge than other cells. Rebalancing is a process that evens out the SOC between cells experiencing advanced deterioration and those experiencing non-advanced deterioration. This allows the battery pack as a whole to achieve performance close to its rated capacity. Rebalancing is therefore a suitable measure for cells experiencing advanced deterioration.

[0030] If battery cell degradation exceeds the level at which rebalancing can restore performance, measures other than rebalancing are required. Reconfiguration is the preferred method for such battery cells. Specifically, the battery cell with advanced deterioration is removed from the battery pack and rebuilt as a recycled unit. More simply, the battery cell with advanced deterioration can be replaced with a new one. In this embodiment, this is also considered a broad term for reconfiguration.

[0031] As a different perspective from the battery cells, measures can also be implemented for the battery pack as a whole. For example, when the SOH of the battery pack as a whole gradually deteriorates, although the battery pack can still be used, it sometimes does not meet the performance requirements under the current usage environment. In such a case, consider switching the battery pack to other usage environments with more relaxed performance requirements. On the contrary, when the SOH of the battery pack as a whole is high enough, consider switching to other usage environments with more stringent performance requirements. The battery pack mentioned here can be a battery module composed of multiple battery cells, a battery pack composed of multiple battery modules, or any other arbitrary unit.

[0032] Repurposing batteries also includes disassembling batteries and extracting materials for recycling. Therefore, the purpose of repurposing batteries also includes recycling purposes, and is treated as "repurposing" in a broad sense, including both.

[0033] When selecting measures to be implemented for degraded batteries, the calculation unit 11 optimizes the economic benefits of these measures. This process determines the batteries for which the measures should be implemented, and optimizes the content and timing of these measures from an economic perspective. The specific optimization method will be described later.

[0034] Figure 3 Indicates the result of predicting the time-dependent change of the SOH of the battery cell. When the degradation of the SOH is relatively small (SOH is above the first threshold), rebalancing can be selected as a measure. When the degradation of the SOH is further aggravated (SOH is below the first threshold and above the second threshold), reconstruction can be selected as a measure. Figure 3 On the vertical axis, the interval selected for rebalancing and the interval selected for reconstruction may or may not be connected. In the case where the two intervals are not connected, the measures implemented in the gap between the two intervals may be, for example, either rebalancing or reconstruction.

[0035] The calculation unit 11 can also be Figure 3 Instead of choosing between rebalancing and restructuring, it is possible to select measures that optimize economic effects. For example, when using diversion as a measure option, the economic effects of diversion can be compared with the economic effects of other measures. Figure 3 For batteries with SOH near the boundary between rebalancing and reconstruction, either rebalancing or reconstruction can be adopted, so the economic effect can be further considered to select which measure to adopt. Figure 3 The method considering economic effects is explained in this paper.

[0036] Figure 4 It is a schematic diagram showing the flow of processing performed by the calculation unit 11. Figure 4 express Figure 2 A specific example of the optimization process in FIG. The calculation unit 11 receives cost data and price data and uses them to optimize (a) the target battery for the measure, (b) the content of the measure, and the time for implementing the measure.

[0037] Cost data describes the costs incurred as a measure is implemented and forecasts the time-varying variations in these costs. Cost data includes labor costs, equipment costs, and other items. Labor costs are defined for each measure, varying over time as a measure is implemented. Equipment costs are defined for each measure, varying over time as a measure is implemented. If the time-varying variations in costs are small, a forecast of these variations is not necessarily necessary. In this case, all costs are assumed to be constant over time. This applies to the price data described below.

[0038] Price data describes battery prices and forecasts of their price fluctuations over time. Price data includes used battery prices, battery material prices, and new battery prices. Used battery prices are the market price of used batteries. Battery material prices are the market price of recycled materials. New battery prices are the market price of new batteries.

[0039] The calculation unit 11 uses the cost data and price data to estimate the economic effect of a measure. For example, the calculation unit 11 uses the cost data and price data to calculate the economic effect of rebalancing a battery cell at that time. Furthermore, the calculation unit 11 uses the cost data and price data to calculate the economic effect of reconfiguring the battery cell at that time. Furthermore, the calculation unit 11 uses the cost data and price data to calculate the economic effect of switching the battery cell to another one at that time.

[0040] The economic benefits of rebalancing are determined, for example, by the costs associated with performing rebalancing and the increased economic value of the battery due to the extended battery lifespan. Costs can be calculated based on cost data. The increased economic value can be evaluated using an arbitrary evaluation function based on the increase in battery lifespan and the fluctuation in battery prices over time.

[0041] The economic benefits of a reconfiguration are determined, for example, by the costs associated with performing the reconfiguration and the increased economic value of the battery due to the extended battery lifespan. Costs can be calculated based on cost data and price data. Specifically, the cost of replacing deteriorated battery cells with new or used ones is calculated by referring to used or new battery prices. The increased economic value can be evaluated using any evaluation function based on the increase in battery lifespan and the fluctuation in battery prices over time.

[0042] The economic effect of the diversion is determined, for example, by the costs incurred as the diversion is implemented and the benefits obtained through the diversion. Regarding the benefits, for example, in the case of selling to other companies, it can be calculated based on price data. Regarding the costs (including labor costs, transportation costs, etc. required for sales), it can be calculated based on cost data. In the case of the operator's own internal diversion purpose, it is determined by the cost required to discard the existing batteries at the diversion destination and the economic value of the batteries increased due to the extension of the battery life at the diversion destination (the number of years of continued use of the converted batteries is extended).

[0043] The calculation unit 11 estimates the economic benefits of each measure for each implementation period. Based on the results, the calculation unit 11 optimizes the measures to be implemented and the implementation period of the measures. For example, for a battery, by comparing (a) the economic benefits of immediate conversion, (b) the economic benefits of continued use to the end of its life through rebalancing or reconstruction, and (c) the economic benefits of continued use after rebalancing or reconstruction for a certain period before conversion, the measure with the greatest economic benefit and the implementation period are determined.

[0044] <Implementation 1: Summary>

[0045] The battery degradation degree management system 1 according to the first embodiment optimizes the measures to be taken as the battery SOH decreases and the timing of their implementation based on the time-varying cost. This optimizes the economic effect of the measures taken as the battery deteriorates from a cost perspective.

[0046] The battery degradation management system 1 of the first embodiment optimizes the measures to be implemented as the battery's SOH decreases and the timing of implementing these measures based on time-varying costs and battery market prices. This optimizes the economic effectiveness of measures implemented as the battery deteriorates, taking into account market prices and costs. Market prices and costs both fluctuate over time, but according to the first embodiment, by considering the temporal changes in market prices and costs for multiple measures, the optimal measure can be selected, taking into account these fluctuating prices.

[0047] <Implementation Method 2>

[0048] In the first embodiment, the Figure 3 Selecting which of rebalancing and reconstruction to perform, or selecting a measure that optimizes economic benefits. In the second embodiment of the present invention, another method of selecting a measure will be described. The configuration of the battery degradation degree management system 1 is the same as that of the first embodiment.

[0049] The calculation unit 11 first calculates the SOH amount that can be restored by rebalancing for each battery cell. The calculation unit 11 calculates the economic effect of rebalancing for each battery cell using the method described in Implementation 1. For battery cells with sufficient economic effects (economic effects above the threshold value that can be foreseen), rebalancing is selected as a measure. Otherwise, the process proceeds to the following steps. The battery cells that are the subject of this step may also be only those whose SOH is significantly restored (the increased SOH amount is above the threshold value) by rebalancing.

[0050] Figure 5 The diagram shows the results of measuring the SOH of each battery cell. The calculation unit 11 determines whether the SOH of the battery cell that is not selected for rebalancing is less than a threshold value. Figure 5 Among them, there is one battery cell with an SOH below a threshold. The calculation unit 11 calculates the economic benefit of reconfiguring this battery cell using the method described in Embodiment 1. If the economic benefit is sufficient (an economic benefit exceeding the threshold is foreseeable), reconfiguration is selected as the measure for this battery cell. Otherwise, diversion is selected as the measure for this battery cell.

[0051] The method described in the first embodiment estimates the economic effects of all measures at each implementation period, making it possible to optimize measures and their implementation periods. However, this method results in a high computational load. The method of the second embodiment prioritizes measures in the order of rebalancing => reconstruction => diversion, thus reducing the computational load compared to the first embodiment.

[0052] As a preliminary consideration when selecting measures, the calculation unit 11 may also consider environmental load. For example, it may be possible to obtain environmental load data that describes indices indicating the environmental load incurred by implementing a measure and then increase or decrease the economic impact of the measure based on the indices described in the data. The calculation unit 11 then selects a measure based on the resulting economic impact.

[0053] <Implementation Method 3>

[0054] In the third embodiment of the present invention, a method of estimating the SOH of a battery will be described. The configuration of the battery deterioration degree management system 1 is the same as that of the first and second embodiments.

[0055] Patent Document 2 describes a method that calculates a function representing battery pack degradation based on the battery capacity of the battery pack and uses this function to estimate the rate of degradation and the replacement period. Because the rate of degradation corresponds to the state of health (SOH), this method can be used to estimate the battery's state of health (SOH). This method estimates the battery's degradation state based on the temporal change in SOC.

[0056] Specifically, first, the measured values ​​of the battery voltage, battery current, and battery temperature are obtained. The SOC-OCV curve and the SOC-charging resistance curve are further referred to. The SOC can be calculated by time-integrating the battery current. Since the charging resistance has a temperature characteristic, the charging resistance can be obtained by using the SOC and the battery temperature and referring to the SOC-charging resistance curve. The relationship between OCV and SOC can be obtained from the SOC-OCV curve. The relationship between the battery voltage and OCV can be calculated based on the charging resistance and the battery current. Convergence calculation is performed until the difference between the calculated battery voltage and its measured value becomes sufficiently small. Furthermore, the discharge resistance is obtained by referring to the SOC-discharge resistance curve, and the SOC when the discharge is stopped is calculated using the discharge resistance. Based on the difference between the SOC after charging and the SOC after discharging, the battery capacity of the battery can be calculated. Furthermore, based on the time series change of the capacity, an approximate function representing the degradation rate is calculated. This is because the battery capacity gradually decreases as the battery deteriorates. The calculation unit 11 can use this method to estimate the SOH.

[0057] The calculation unit 11 can also replace the method of patent document 2 or be used in conjunction with it to estimate the SOH based on the measurement results of the battery output. For example, the method described in WO2022 / 024235A1 can be used. In this document, the variation of the battery voltage during the rest period after the charging or discharging action is obtained, and the variation is used to estimate the SOH. For example, the relatively sharp voltage variation (first difference) in the period just after the charging and discharging is stopped is correlated with the internal resistance of the battery, and the relatively gentle voltage variation (second difference) in the subsequent period is correlated with the SOH of the battery.

[0058] Therefore, in this document, first data describing the relationship between the first difference and internal resistance and second data describing the relationship between the second difference and SOH are pre-acquired. The internal resistance and SOH are estimated by referring to these data using the measured values ​​of the first and second differences. This method can estimate SOH in a relatively short time. The calculation unit 11 can use this method to estimate SOH.

[0059] <Regarding Modifications of the Invention>

[0060] The present invention is not limited to the above-described embodiments and includes various variations. For example, the above-described embodiments are described in detail to facilitate understanding of the present invention and are not necessarily limited to having all the structures described. In addition, a portion of the structure of a certain embodiment can be replaced with the structure of another embodiment, and the structure of another embodiment can be added to the structure of a certain embodiment. In addition, with respect to a portion of the structure of each embodiment, other structures can be added, deleted, or replaced.

[0061] In the above embodiment, the calculation unit 11 may be configured by hardware such as a circuit device implementing its functions, or may be configured by a calculation device such as a CPU (Central Processing Unit) executing software implementing its functions.

[0062] While the above embodiments describe examples where measures are implemented for each battery cell, the targets for implementation are not limited to cells. For example, measures may be implemented for each battery module comprised of multiple battery cells, or for each battery pack comprised of multiple battery modules. A combination of these is also possible.

[0063] In the above embodiment, the following items are considered as cost items or benefit items used when calculating the economic effect of a measure, but the present invention is not limited thereto.

[0064] Reduction in asset maintenance costs: The need for regular repairs and replacements is reduced, reducing maintenance costs. Reduction in investment: The time until a new asset of the same type is purchased is extended, reducing investment.

[0065] Improved cash flow: By reducing investment and maintenance costs, cash flow can be improved, ensuring funds that contribute to business stability and future growth;

[0066] Increase in selling price: By implementing measures to suppress deterioration, the selling price is increased.

[0067] Description of Reference Numerals

[0068] 1: Battery degradation management system

[0069] 11: Operation unit

[0070] 12: Storage unit.

Claims

1. A battery degradation management system, characterized in that: The battery degradation management system includes: a calculation unit that estimates a degradation state of the plurality of batteries; and a storage unit that stores data used by the computing unit, The calculation unit determines a battery among the plurality of batteries for which a measure to reduce the degradation state is required, The calculation unit calculates the cost required to implement the measure based on cost data describing at least one of a temporal change in cost associated with implementing the measure and a prediction of the temporal change in cost. The calculation unit determines a measure that can maximize economic effects among the plurality of measures and a time to implement the measure based on the calculated cost.

2. The battery degradation management system according to claim 1, wherein: The measure is at least one of rebalancing to equalize the charge states of the plurality of batteries, reconstruction to regenerate the batteries, and diverting the batteries to other uses having different performance requirements.

3. The battery degradation management system according to claim 2, wherein: When the degradation state is equal to or greater than a first threshold, the calculation unit selects the rebalancing as the measure. The calculation unit selects the reconstruction as the measure when the degradation state is equal to or lower than the first threshold and equal to or higher than a second threshold.

4. The battery degradation management system according to claim 2, wherein: When the degradation state of the plurality of batteries as a whole is equal to or greater than a third threshold, the calculation unit selects, as the measure, diversion to the other use having a higher performance requirement level than the current operating environment of the plurality of batteries; When the degradation state of the plurality of batteries as a whole is equal to or smaller than a fourth threshold value that is lower than the third threshold value, the calculation unit selects, as the measure, diversion to the other use having a lower performance requirement level than the current operating environment of the plurality of batteries.

5. The battery degradation management system according to claim 1, wherein: The cost data describes at least one of a labor cost that varies over time and a facility cost that varies over time as the measure is implemented, as the cost. The calculation unit calculates the economic effect using at least one of the time-varying labor cost described in the cost data and the time-varying equipment cost described in the cost data.

6. The battery degradation management system according to claim 2, wherein: The cost data describes at least one of a labor cost that varies over time and a facility cost that varies over time as the measure is implemented, as the cost. The calculation unit calculates the economic effect by calculating the cost required to implement the rebalancing, the reconstruction, or the conversion using at least one of the time-varying labor cost described in the cost data and the time-varying equipment cost described in the cost data.

7. The battery degradation management system according to claim 1, wherein: The calculation unit calculates the economic effect based on price data describing at least one of a temporal change in price of the battery and a prediction of the temporal change in price.

8. The battery degradation management system according to claim 2, wherein: The calculation unit calculates the economic effect based on price data describing at least one of a temporal change in the price of the battery and a prediction of the temporal change in the price. The price data describes at least one of the market price of used batteries, the market price of battery materials, the market price of new batteries, and a forecast of temporal changes in these prices. The calculation unit calculates the economic effects of each of the rebalancing, the reconstruction, and the diversion based on each of the prices described in the price data or a forecast of the temporal change of the prices, thereby determining which of the rebalancing, the reconstruction, and the diversion should be implemented as the measure.

9. The battery degradation management system according to claim 2, wherein: The calculation unit calculates the economic effect based on price data describing at least one of a temporal change in the price of the battery and a prediction of the temporal change in the price. If the economic effect of the rebalancing is equal to or greater than a fifth threshold, the calculation unit selects the rebalancing as the measure; If the economic effect of the rebalancing is smaller than the fifth threshold, the calculation unit selects either the reconstruction or the diversion as the measure.

10. The battery degradation management system according to claim 9, wherein: If the economic effect of the reconstruction is equal to or greater than a sixth threshold, the calculation unit selects the reconstruction as the measure, If the economic effect of the reconstruction is smaller than the sixth threshold, the calculation unit selects the diversion as the measure.

11. The battery degradation management system according to claim 1, wherein: The calculation unit determines the content of the measure to be implemented based on environmental load data describing an index indicating an environmental load generated by implementation of the measure.

12. The battery degradation management system according to claim 1, wherein: The calculation unit obtains SOC-OCV data describing the relationship between the state of charge of the battery and the open circuit voltage of the battery, SOC-charge resistance data describing the relationship between the state of charge of the battery and the charge resistance of the battery, and SOC-discharge resistance data describing the relationship between the state of charge of the battery and the discharge resistance of the battery. The calculation unit estimates a deterioration state of the battery by referring to the SOC-OCV data, the SOC-charge resistance data, and the SOC-discharge resistance data to estimate a temporal change in battery capacity of the battery.

13. The battery degradation management system according to claim 12, wherein: The calculation unit obtains measurement values ​​of the voltage output by the battery, the current output by the battery, and the temperature of the battery. The calculation unit calculates the state of charge of the battery by integrating the current over time. The calculation unit obtains the open circuit voltage of the battery and the charging resistance of the battery by using the state of charge and referring to the SOC-OCV data and the SOC-charging resistance data, and corrects the charging resistance using the temperature. The calculation unit estimates the voltage using the charging resistance and the open circuit voltage. The calculation unit calculates the battery capacity by calculating the SOC when discharging is stopped using the SOC-discharge resistance data.

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