Vehicle and battery degradation estimation method

Abstract

To improve the accuracy of estimating the degree of degradation of batteries installed in vehicles. [Solution] The State of Charge (SOC) of the battery 41 is controlled by the ECU 100 so that it does not fall below a lower limit while the vehicle 1 is running. Before starting to charge the battery 41, the ECU 100 performs a discharge process to discharge the battery 41 so that the SOC of the battery 41 becomes a first SOC or lower, which is lower than the lower limit. After the discharge process, the ECU 100 performs a charge process to charge the battery 41 so that the SOC of the battery 41 reaches a second SOC, which is higher than the SOC before the discharge process. Based on the first SOC, the second SOC, and the cumulative value of the charging current of the battery 41 from the start to the end of the charge process, the ECU 100 calculates an estimated value of the current full charge capacity of the battery 41. Based on this estimated value and the initial full charge capacity of the battery 41, the ECU 100 estimates the State of Health (SOH) of the battery 41.

Description

Technical Field

[0001] The present disclosure relates to a vehicle and a method for estimating deterioration of a battery.

Background Art

[0002] Japanese Patent Application Laid-Open No. 2004-166350 discloses a battery control device that charges with an internal combustion engine when the SOC (State Of Charge) of a secondary battery (battery) reaches a lower limit value and stops charging the secondary battery when the SOC reaches an upper limit value.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The degree of deterioration of a battery mounted on a vehicle affects the charging time of the battery. Therefore, it is required to accurately estimate the degree of deterioration of the battery mounted on the vehicle.

[0005] The present disclosure has been made to solve the above problems, and one of the objects of the present disclosure is to improve the estimation accuracy of the degree of deterioration of a battery mounted on a vehicle.

Means for Solving the Problems

[0006] (1) A vehicle that can be charged by connecting to an external device, relating to a certain aspect of the present disclosure, comprises a first battery that is charged by power supplied from the external device, and a control device that manages the first battery so that the State of Charge (SOC) of the first battery does not fall below a lower limit when the vehicle is running. Before starting to charge the first battery, the control device performs a discharge process to discharge the first battery so that the SOC of the first battery becomes less than or equal to a first SOC, which is lower than the lower limit. After the discharge process, the control device performs a charge process to charge the first battery with power supplied from the external device so that the SOC of the first battery reaches a second SOC, which is higher than the SOC before the discharge process started. The control device calculates an estimated value of the current full charge capacity of the first battery based on the first SOC, the second SOC, and the cumulative value of the charging current of the first battery from the start to the end of the charge process. The control device estimates the State of Health (SOH) of the first battery based on the estimated value and the initial full charge capacity of the first battery in its initial state.

[0007] (2) The external device connected to the vehicle described in (1) above is a rapid charger capable of rapid charging. The discharge process includes discharging from the first battery to the external device.

[0008] (3) The vehicle described in (1) above further comprises a second battery which is charged by power supplied from the first battery. The discharge process includes discharging from the first battery to the second battery.

[0009] (4) In any of the vehicles described in (1) to (3) above, the first SOC is zero percent.

[0010] (5) In other aspects of the Disclosure, a method for estimating the degradation of a vehicle-mounted battery that can be charged by connecting to an external device is provided. The battery's State of Charge (SOC) is controlled so as not to fall below a lower limit while the vehicle is running. The degradation estimation method includes: performing a discharge process to discharge the battery before charging begins so that the SOC of the battery is below a first SOC, which is lower than the lower limit; performing a charge process after the discharge process so that the battery's SOC reaches a second SOC, which is higher than the SOC before the discharge process began; calculating an estimate of the battery's current full charge capacity based on the first SOC, the second SOC, and the cumulative value of the battery's charging current from the start to the end of the charge process; and estimating the battery's State of Health (SOH) based on the estimate and the initial full charge capacity of the battery in its initial state. [Effects of the Invention]

[0011] According to this disclosure, it is possible to improve the accuracy of estimating the degree of degradation of batteries installed in vehicles. [Brief explanation of the drawing]

[0012] [Figure 1] This is a block diagram showing an example of the overall configuration of a vehicle according to this embodiment. [Figure 2] This diagram illustrates the usable range of the State of Charge (SOC) of the battery 41 while vehicle 1 is in operation. [Figure 3] This diagram illustrates the usable range of the State of Charge (SOC) of the battery 41 during charging of vehicle 1. [Figure 4] This diagram illustrates the overview of the degradation estimation process according to this embodiment. [Figure 5] This flowchart shows an example of the processing procedure for the degradation estimation process according to this embodiment. [Figure 6] This is a block diagram showing an example of the overall configuration of a modified vehicle. [Modes for carrying out the invention]

[0013] Hereinafter, embodiments and modifications of the present disclosure will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and their descriptions will not be repeated.

[0014] [Embodiment] <Vehicle configuration> Figure 1 is a block diagram showing an example of the overall configuration of a vehicle according to this embodiment. Vehicle 1 is a vehicle that can be charged by connecting to an external device 902 installed outside of Vehicle 1. Vehicle 1 is, for example, an electric vehicle (BEV: Battery Electric Vehicle). Vehicle 1 may be any vehicle configured to enable external charging, and may be, for example, a plug-in hybrid electric vehicle (PHEV: Plug-in Hybrid Electric Vehicle). The external device 902 is a fast charger capable of rapid charging and rapid discharging. The external device 902 converts AC power supplied from the commercial power supply 903 into DC power and supplies the DC power to Vehicle 1 (external charging). The external device 902 is configured to communicate with the ECU (Electronic Control Unit) 100, which will be described later.

[0015] Vehicle 1 includes an inlet 10, a charging relay 30, a battery 41, a monitoring unit 50, a PCU (Power Control Unit) 80, a motor generator 90, and an ECU 100.

[0016] The inlet 10 is configured to allow insertion of a charging connector provided at the end of the charging cable 901. The vehicle 1 is configured to enable "external charging," which charges the battery 41 using power supplied from an external device 902 via the charging cable 901. The vehicle 1 is also configured to enable "external power supply," which supplies power from the vehicle 1 to the external device 902 via the charging cable 901.

[0017] The charging relay 30 is electrically connected to the power line connecting the inlet 10 and the battery 41. The charging relay 30 is opened and closed according to control commands from the ECU 100.

[0018] The battery 41 is a battery pack including a plurality of cells. Each cell is a storage battery (secondary battery) such as a lithium-ion battery or a nickel-metal hydride battery. The battery 41 is charged by the power supplied from the external device 902 and stores the power for driving the motor generator 90. The battery 41 supplies power to the motor generator 90 through the PCU 8 (should it be 80?). The battery 41 corresponds to the "first battery" according to the present disclosure.

[0019] The monitoring unit 50 includes a voltage sensor 51, a current sensor 52, and a temperature sensor 53. The voltage sensor 51 detects the voltage V of the battery 41. The current sensor 52 detects the current I flowing through the battery 41. The temperature sensor 53 detects the temperature T of the battery 41. Each sensor outputs a signal indicating its detection result to the ECU 100.

[0020] The PCU 80 (should it be 80?) drives the motor generator 90 according to a control command from the ECU 100.

[0021] The motor generator 90 is a traveling motor generator that rotates a drive shaft using the power supplied from the battery 41.

[0022] The ECU 100 includes a processor 101 such as a CPU (Central Processing Unit), and a memory 102 such as a ROM (Read Only Memory) and a RAM (Random Access Memory). In the memory 102, a map (for example, an SOC-OCV (Open Circuit Voltage) curve) and a program are stored. The SOC-OCV curve indicates the SOC of the battery 41 corresponding to the open circuit voltage of the battery 41.

[0023] It should be noted that there seems to be a potential error in the text where "PCU80" and "PCU8" are mentioned inconsistently. I've translated it as best as possible while keeping the text tags intact.The ECU 100 manages the battery 41 based on signals from each sensor of the monitoring unit 50 and maps and programs stored in the memory 102. When the vehicle 1 is running, the ECU 100 manages the battery 41 so that its State of Charge (SOC) does not fall below a lower limit. In this embodiment, a major process performed by the ECU 100 is the "degradation estimation process" which estimates the degree of degradation of the battery 41. The degree of degradation of the battery 41 is the degree of decrease in the capacity (full charge capacity) of the battery 41. The ECU 100 also controls the equipment (charging relay 30 and PCU 80) so that the vehicle 1 reaches a desired state based on signals from each sensor provided in the vehicle 1 and maps and programs stored in the memory. The ECU 100 corresponds to the "control device" in this disclosure.

[0024] <Usable range of the State of Charge (SOC) of battery 41 during vehicle 1 operation> Figure 2 is a diagram illustrating the usable range of the State of Charge (SOC) of battery 41 during vehicle 1 operation. Graph G1 is an example of the SOC-OCV curve of battery 41 stored in memory 102.

[0025] To prevent overcharging and over-discharging of the battery 41, vehicle 1 has defined restricted areas for the battery 41's State of Charge (SOC) during vehicle operation: an area where the SOC is less than x%, and an area where the SOC is greater than y%. The usable range of the battery 41's SOC during vehicle operation is set to an area where the SOC is x% or greater and y% or less. In other words, in vehicle 1, the lower limit of the battery 41's driving SOC is set to x%, and the upper limit of the battery 41's driving SOC is set to y%. x% is, for example, a value between 15% and 20%, and y% is, for example, a value between 90% and 95%. Driving SOC refers to the battery 41's State of Charge (SOC) during vehicle operation (when external charging is not performed, and including when vehicle 1 is stopped, parked, etc.).

[0026] As can be seen from Graph G1, in the region where SOC use is prohibited, the amount of OCV change per unit SOC (the rate of change in the SOC-OCV curve) is larger compared to the region where SOC use is permitted.

[0027] <Usable range of SOC during charging of vehicle 1> Figure 3 is a diagram illustrating the usable range of the State of Charge (SOC) of the battery 41 during charging of vehicle 1. In vehicle 1, the lower limit of the charging SOC is set to a lower value than the lower limit of the driving SOC. The charging SOC is the State of Charge of the battery 41 when vehicle 1 is externally charged. In this embodiment, the lower limit of the charging SOC is set to zero percent, which is lower than the lower limit of the driving SOC (i.e., x%). On the other hand, the upper limit of the charging SOC is set to the same value as the upper limit of the driving SOC (i.e., y%). In other words, in vehicle 1, the usable range of the SOC of the battery 41 during external charging of vehicle 1 is set to a range where the SOC is 0 percent or more and y percent or less. In addition, in vehicle 1, the range where the SOC is higher than y percent is set as the prohibited range of the SOC of the battery 41 during external charging of vehicle 1. As a result, in vehicle 1, the usable range of the SOC during external charging is wider than the usable range of the SOC during driving.

[0028] Furthermore, the lower limit of the charging SOC can be any value lower than the lower limit of the driving SOC, and is not limited to zero percent.

[0029] <Degradation estimation process> The ECU100 performs a "degradation estimation process" to estimate the State of Health (SOH) of the battery 41.

[0030] SOH is an indicator of the degree of battery degradation. SOH is expressed as the ratio of the battery's current full charge capacity to its initial full charge capacity in its initial state. The closer the SOH is to zero percent, the more the battery has degraded. The battery's current full charge capacity is estimated based on the SOC at the start of charging, the SOC at the end of charging, and the cumulative charging current of the battery from the start to the end of charging.

[0031] Figure 4 is a diagram illustrating the overview of the degradation estimation process according to this embodiment. When the external device 902 receives an instruction from the user to start external charging, the ECU 100 performs a discharge process before starting external charging. The discharge process involves discharging the battery 41 so that the State of Charge (SOC) of the battery 41 becomes less than or equal to a first SOC, which is lower than the lower limit of the driving SOC. The first SOC is, for example, the same value as the lower limit of the charging SOC. In this embodiment, the first SOC is 0%. Note that the first SOC only needs to be lower than the lower limit of the driving SOC and greater than or equal to the lower limit of the charging SOC, and may be a non-zero value.

[0032] After the discharge process, the ECU 100 performs a charge process. The charge process involves externally charging the battery 41 with power supplied from the external device 902 so that the state of charge (SOC) of the battery 41 reaches a second SOC that is higher than the pre-discharge SOC of the battery 41. The pre-discharge SOC is the state of charge of the battery 41 before the start of the discharge process. For example, the pre-discharge SOC is the SOC of the battery 41 when the ECU 100 receives a signal (hereinafter referred to as the "charge message") transmitted from the external device 902 to the ECU 100 when the external device 902 receives an instruction from the user to start external charging. The second SOC is the end value of the external charge and is specified by the user. The user can specify any value as the second SOC that is higher than the pre-discharge SOC and less than or equal to the upper limit of the charge SOC.

[0033] For example, if the pre-discharge state of charge (SOC) is P%, and the user specifies a charge termination value higher than P%, the ECU 100 first reduces the SOC of the battery 41 from P% to a first SOC (zero%) through a discharge process. After the discharge process, the ECU 100 increases the SOC of the battery 41 to Q% through a charge process.

[0034] By performing a discharge process before external charging begins, the State of Charge (SOC) at the start of external charging can be made lower than the SOC of battery 41 when the ECU 100 receives a charging message. Therefore, when a discharge process is performed before external charging begins, the difference between the SOC at the start of charging and the SOC at the end of charging is larger than when external charging begins without a discharge process.

[0035] Generally, the smaller the difference between the State of Charge (SOC) at the start of charging and the SOC at the end of charging, the greater the influence of detection errors by the voltage and current sensors, which can lead to a larger difference between the estimated SOH and the actual SOH. In other words, the smaller the difference between the SOC at the start of charging and the SOC at the end of charging, the lower the accuracy of SOH estimation. Conversely, the larger the difference between the SOC at the start of charging and the SOC at the end of charging, the higher the accuracy of SOH estimation. According to this embodiment, a discharge process is performed before the start of external charging, and the difference between the SOC at the start of charging and the SOC at the end of charging of the battery 41 becomes larger, thereby improving the accuracy of estimating the degree of degradation (SOH) of the battery 41.

[0036] Figure 5 is a flowchart showing an example of the processing procedure for degradation estimation according to this embodiment. The process shown in this flowchart is executed when the ECU 100 detects that the charging connector provided at the tip of the charging cable 901 has been inserted into the inlet 10 and receives a charging message. Each step is implemented by software processing by the ECU 100, but may also be implemented by hardware (electrical circuits) located within the ECU 100. Hereinafter, each step will be abbreviated as S.

[0037] In S1, the processor 101 calculates the current State of Charge (SOC) of the battery 41. The SOC can be calculated, for example, using a method involving the integration of current values. Specifically, when the vehicle 1 is started, the processor 101 uses the voltage detected by the voltage sensor 51 as the open-circuit voltage, identifies the SOC corresponding to the open-circuit voltage from the SOC-OCV curve stored in the memory 102, and stores the identified SOC in the memory 102 as the SOC of the battery 41 at the time of vehicle 1's startup (hereinafter referred to as "startup SOC"). In S1, the processor 101 calculates the change in the SOC of the battery 41 from the time of vehicle 1's startup to the present using a method involving the integration of current values, and determines the current SOC of the battery 41 by adding this change to the startup SOC. The SOC calculated in S1 is an example of the "pre-discharge SOC of battery 41" described above.

[0038] Next, in S2, the processor 101 starts discharging the battery 41 and integrating the current of the battery 41. Specifically, first, the processor 101 sends an instruction to the external device 902 to switch to the external power supply mode, which receives power supplied from the vehicle 1. When the processor 101 receives notification from the external device 902 that the switch to the external power supply mode is complete, it closes the charging relay 30 and starts integrating the current. As the external device 902 switches to the external power supply mode and the charging relay 30 closes, the battery 41 starts discharging to the external device 902.

[0039] Next, in S3, the processor 101 determines whether the SOC of the battery 41 is less than or equal to the first SOC. As described above, in this embodiment, the first SOC is zero percent. If the SOC of the battery 41 is less than or equal to the first SOC (YES in S3), the processor 101 proceeds to S4. If the SOC of the battery 41 is not less than or equal to the first SOC (NO in S3), the processor 101 returns to S2. In the second and subsequent S2s, the processor 101 continues to discharge the battery 41 and integrate the current. S2 and S3 correspond to the "discharge process" according to this disclosure.

[0040] In S4, the processor 101 stops discharging the battery 41 by sending an instruction to the external device 902 to terminate the external power supply mode. Also in S4, the processor 101 stops current integration.

[0041] Next, in S5, the processor 101 starts charging the battery 41 and integrating the current. Specifically, first, the processor 101 sends an instruction to the external device 902 to switch to the external charging mode, which supplies power to the vehicle 1. When the processor 101 receives a notification from the external device 902 indicating that the switch to the external charging mode is complete, the processor 101 starts integrating the current.

[0042] Next, in S6, the processor 101 determines whether the SOC of the battery 41 is equal to or greater than the second SOC. As described above, the second SOC is the termination value of external charging specified by the user. If the SOC of the battery 41 is equal to or greater than the second SOC (YES in S6), the processor 101 proceeds to S7. If the SOC of the battery 41 is not equal to or greater than the second SOC (NO in S6), the processor 101 returns to S5. In subsequent S5s, the processor 101 continues charging the battery 41 and integrating the current. S5 and S6 correspond to the "charging process" as described in this disclosure.

[0043] In S7, the processor 101 stops charging the battery 41 and integrating current. Specifically, first, the processor 101 sends an instruction to the external device 902 to terminate the external charging mode. This stops the power supply from the external device 902 to the battery 41. Next, the processor 101 opens the charging relay 30 and stops integrating current.

[0044] Next, in S8, the processor 101 calculates an estimated value of the current full charge capacity of the battery 41 based on the first SOC, the second SOC, and the integrated value of the charging current of the battery 41 from the start to the end of the charging process. Specifically, first, the processor 101 obtains the open-circuit voltage corresponding to the first SOC from the SOC-OCV curve stored in memory 102 as the open-circuit voltage at the start of charging. Next, the processor 101 obtains the open-circuit voltage corresponding to the second SOC from the SOC-OCV curve stored in memory 102 as the open-circuit voltage at the end of charging. Then, the processor 101 calculates an estimated value of the current full charge capacity of the battery 41 based on the open-circuit voltage at the start of charging, the open-circuit voltage at the end of charging, and the integrated value of the charging current of the battery 41 from the start to the end of the charging process.

[0045] Next, in S9, the processor 101 estimates the State of Health (SOH) of the battery 41 based on the estimated value calculated in S8 and the initial full charge capacity of the battery 41 in its initial state. The initial full charge capacity is stored in memory 102 beforehand. Specifically, the processor 101 calculates the estimated value of SOH [%] using the current estimated full charge capacity of the battery 41 Ces [Ah], the initial full charge capacity Co [Ah], and the following predetermined formula (1).

[0046] SOH=Ces / Co×100...Equation (1)

[0047] After S9, processor 101 terminates the degradation estimation process.

[0048] Thus, in this embodiment, before starting to charge the battery 41, the processor 101 performs a discharge process to discharge the battery 41 so that the state of charge (SOC) of the battery 41 becomes a first SOC or lower, which is lower than the lower limit of the driving SOC. After the discharge process, the processor 101 performs a charge process to charge the battery 41 with power supplied from the external device 902 so that the SOC of the battery 41 reaches a second SOC, which is higher than the SOC before the discharge process started. Therefore, the SOC of the battery 41 at the start of charging can be lower than the SOC of the battery 41 when the ECU 100 receives a charge message. Consequently, according to this embodiment, the difference between the SOC at the start of the charging process and the SOC at the end of the charging process is larger than when the charging process is started without a discharge process. Therefore, according to this embodiment, the estimation accuracy of the degree of degradation (SOH) of the battery 41 is improved.

[0049] In this embodiment, the external device 902 is a rapid charger, and the discharge process includes discharging from the battery 41 to the external device 902. According to this embodiment, the time from when the ECU 100 receives a charging message until the battery 41 is fully charged is longer than when charging of the battery 41 is started without discharging the battery 41, by the amount of the battery 41's discharge time. However, since the external device 902 is a rapid charger, the charging time of the battery 41 can be reduced compared to when the external device 902 is a normal charger. Therefore, according to this embodiment, the time from when the ECU 100 receives a charging message until the battery 41 is fully charged can be reduced compared to when the external device 902 is a normal charger.

[0050] In this embodiment, the first SOC is zero percent. Therefore, the SOC at the start of charging of the battery 41 can be kept as low as possible. Accordingly, according to this embodiment, the difference between the SOC at the start of the charging process and the SOC at the end of the charging process is maximized, which further improves the accuracy of estimating the degree of degradation (SOH) of the battery 41.

[0051] As shown in Figure 2, the rate of change in the SOC-OCV curve is larger in the SOC non-use region compared to the SOC usable region. Therefore, by setting the first SOC to the non-use region (low SOC region), the amount of OCV change from the start to the end of the charging process becomes larger. Consequently, the accuracy of estimating the current full charge capacity at S8 is improved. As a result, the accuracy of estimating the degree of degradation (SOH) of the battery 41 is improved.

[0052] Vehicle 1 may be configured to be charged by connecting to a standard charger installed in a typical household. Even when a standard charger is connected to vehicle 1, a charging process may be performed after the discharge process. Specifically, before charging of battery 41 begins, processor 101 performs a discharge process to discharge battery 41 to the standard charger so that the state of charge (SOC) of battery 41 becomes a first SOC or lower, which is lower than the lower limit of the driving SOC. After the discharge process, processor 101 performs a charging process to charge battery 41 with power supplied from the standard charger so that the SOC of battery 41 reaches a second SOC, which is higher than the SOC before discharge. This improves the accuracy of estimating the degree of degradation (SOH) of battery 41, even when vehicle 1 is charged by connecting to a standard charger.

[0053] When charging the battery 41 with a standard charger, the charging time is longer than when charging the battery 41 with a fast charger. Therefore, the processor 101 may perform the charging process after the discharge process when a fast charger is connected to the vehicle 1, but may perform the charging process without performing the discharge process when a standard charger is connected to the vehicle 1. This makes it possible to suppress the increase in the time from when the ECU 100 receives a charging message until the battery 41 is fully charged when a standard charger is connected to the vehicle 1.

[0054] [Differentiation] In the above embodiment, during the discharge process, the battery 41 was discharged to the external device 902. In contrast, in the modified example, the vehicle is equipped with other batteries in addition to the battery 41, and during the discharge process, the battery 41 is discharged to the other batteries.

[0055] Figure 6 is a block diagram showing an example of the overall configuration of a modified vehicle. The difference between the modified vehicle 1A and the vehicle 1 (see Figure 1) according to the above embodiment is that vehicle 1A further includes a battery 42. Battery 42 is charged by power supplied from battery 41. Battery 42 may store power to drive the motor generator 90, or it may store power to drive auxiliary equipment mounted on vehicle 1. Battery 42 corresponds to the "second battery" in this disclosure.

[0056] In the modified example, the ECU 100 also performs degradation estimation processing. The difference between the degradation estimation processing in the modified example and the degradation estimation processing in the above embodiment is that the discharge processing in the modified example includes discharging from battery 41 to battery 42. That is, in the discharge processing in the modified example, discharge is performed from battery 41 to battery 42.

[0057] In other respects, the modified vehicle 1A is the same as vehicle 1 according to the above embodiment.

[0058] Thus, in this modified example, during the discharge process, discharge occurs from battery 41 to battery 42. The power stored in battery 42 is used to drive the motor generator 90 or auxiliary equipment. Therefore, according to this modified example, the discharge power of battery 41 can be effectively utilized in vehicle 1A.

[0059] The embodiments and variations disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of this disclosure is indicated by the claims rather than the foregoing description, and all modifications are intended to be within the meaning and scope equivalent to the claims. [Explanation of symbols]

[0060] 1.1A Vehicle, 10 Inlet, 30 Charging Relay, 41,42 Battery, 50 Monitoring Unit, 51 Voltage Sensor, 52 Current Sensor, 53 Temperature Sensor, 80 PCU, 90 Motor Generator, 100 ECU, 101 Processor, 102 Memory, 901 Charging Cable, 902 External Devices, 903 Commercial Power Supply, Ces Estimate, Co Initial Charging Capacity, G1 Graph, I Current, T Temperature, V Voltage.

Claims

1. A vehicle that can be charged by connecting to an external device, A first battery that is charged by power supplied from the external device, The vehicle includes a control device that manages the first battery so that its State of Charge (SOC) does not fall below a lower limit when the vehicle is in operation. The control device is Before starting to charge the first battery, a discharge process is performed to discharge the first battery so that its State of Charge (SOC) becomes less than or equal to a first SOC, which is lower than the lower limit. After the discharge process, a charging process is performed to charge the first battery using power supplied from the external device so that the SOC of the first battery reaches a second SOC that is higher than the SOC before the start of the discharge process. Based on the first SOC, the second SOC, and the integrated value of the charging current of the first battery from the start to the end of the charging process, an estimated value of the current full charge capacity of the first battery is calculated. A vehicle that estimates the State of Health (SOH) of the first battery based on the estimated value and the initial full charge capacity of the first battery in its initial state.

2. The aforementioned external device is a fast charger capable of rapid charging, The vehicle according to claim 1, wherein the discharge process includes discharging from the first battery to the external device.

3. The vehicle further comprises a second battery which is charged by power supplied from the first battery, The vehicle according to claim 1, wherein the discharge process includes discharging from the first battery to the second battery.

4. The vehicle according to any one of claims 1 to 3, wherein the first SOC is zero percent.

5. A method for estimating the degradation of a battery installed in a vehicle that can be charged by connecting to an external device, The State of Charge (SOC) of the aforementioned battery is controlled so as not to fall below a lower limit while the vehicle is running. The aforementioned degradation estimation method is: Before charging of the battery, a discharge process is performed to discharge the battery so that the State of Charge (SOC) of the battery becomes less than or equal to a first SOC, which is lower than the lower limit; After the discharge process, a charging process is performed in which the battery is charged with power supplied from the external device so that the State of Charge (SOC) of the battery reaches a second SOC that is higher than the SOC before the start of the discharge process. Based on the first SOC, the second SOC, and the integrated value of the battery's charging current from the start to the end of the charging process, an estimated value of the battery's current full charge capacity is calculated. A method for estimating battery degradation, comprising estimating the State of Health (SOH) of the battery based on the aforementioned estimated value and the initial capacity of the battery when fully charged in its initial state.

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