Patent Publication Number: US-2023132434-A1

Title: Deterioration diagnosis apparatus of assembled battery and deterioration diagnosis method of assembled battery

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to Japanese Patent Application No. 2021-180364 filed on Nov. 4, 2021, incorporated herein by reference in its entirety. 
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates to a deterioration diagnosis apparatus of an assembled battery and a deterioration diagnosis method of an assembled battery. 
     2. Description of Related Art 
     An assembled battery includes a plurality of secondary batteries electrically connected to each other. By combining the secondary batteries, a large-capacity assembled battery can be obtained. However, a full charge capacity (an electricity amount accumulated in the secondary battery at a time of full charging) of a secondary battery decreases as the secondary battery deteriorates. For example, Japanese Unexamined Patent Application Publication No. 2013-110906 (JP 2013-110906 A) discloses a deterioration diagnosis method of an assembled battery that executes discharging until a voltage (a voltage between terminals) of the assembled battery reaches a predetermined discharging end voltage, and estimates a deterioration degree of the assembled battery using data (a discharging curve) indicating a transition of the voltage of the assembled battery during the discharging. 
     SUMMARY 
     In the deterioration diagnosis method of the assembled battery described in JP 2013-110906 A, the discharging end voltage is set in advance so as to ensure sufficient diagnosis accuracy while avoiding over-discharging of the assembled battery. The over-discharging of the assembled battery means excessive discharging to an extent that deterioration of the assembled battery progresses. 
     When the deterioration diagnosis of the assembled battery is executed by the method described in JP 2013-110906 A in a vehicle including an internal combustion engine, a motor that executes start processing (for example, cranking) of the internal combustion engine, and an assembled battery that supplies power to the motor, discharging of the assembled battery may be continued even when the assembled battery becomes unable to supply power required for the start processing of the internal combustion engine to the motor. For this reason, it may take time and effort to charge the assembled battery with an external power source (a power source outside the vehicle) after an end of the diagnosis. 
     The present disclosure provides a deterioration diagnosis apparatus and a deterioration diagnosis method of an assembled battery that can easily execute start processing of an internal combustion engine after discharging for the deterioration diagnosis of the assembled battery is executed in a vehicle including an internal combustion engine, a motor that executes the start processing of the internal combustion engine, and an assembled battery that supplies power to the motor. 
     A deterioration diagnosis apparatus of the assembled battery according to a first aspect of the present disclosure includes at least one processor. The at least one processor is configured to execute discharging of each of a plurality of cells included in the assembled battery mounted on a vehicle while measuring a voltage of each of the cells, and estimate a deterioration degree of the assembled battery using voltage data indicating a transition of a voltage of at least one of the cells from a discharging start voltage to a predetermined discharging end voltage. The vehicle includes an internal combustion engine and a motor that executes start processing of the internal combustion engine. The assembled battery is configured to supply power to the motor. The at least one processor is configured to determine, during the discharging of each of the cells, whether the assembled battery becomes unable to supply power required for the start processing to the motor when the discharging is continued, and end the discharging before the assembled battery becomes unable to supply the power required for the start processing to the motor. 
     With the above configuration, the discharging is ended before the assembled battery becomes unable to supply the power required for the start processing to the motor. For this reason, the motor can receive power supplied from the assembled battery after an end of the discharging and execute the start processing of the internal combustion engine. As such, with the deterioration diagnosis apparatus of the assembled battery, it is possible to easily execute the start processing of the internal combustion engine after the discharging for the deterioration diagnosis of the assembled battery is executed. 
     The cell is a secondary battery composing the assembled battery. The assembled battery is composed of the cells electrically connected to each other. The start processing is processing for starting the internal combustion engine. The internal combustion engine can be started by receiving assistance from the motor. The start processing may be cranking. The cranking is to start the internal combustion engine by rotating a crankshaft of the internal combustion engine. 
     In the first aspect, the at least one processor may be configured to, during the discharging of each of the cells, at a time at which an average value or a median value of voltages of all the cells included in the assembled battery becomes a predetermined value or lower, determine that the assembled battery becomes unable to supply the power required for the start processing to the motor when the discharging is continued after the time, and end the discharging. 
     With the above configuration, it is easy for the at least one processor to accurately determine whether the assembled battery becomes unable to supply the power required for the start processing to the motor when the discharging is continued. Further, since the average value or the median value of the voltages of all the cells is used for the determination, a sensor that measures a voltage between terminals of the assembled battery is unnecessary. The predetermined value may be a voltage value required for the motor to execute the start processing of the internal combustion engine. The predetermined value may be a fixed value or may be variable depending on a situation. 
     In the first aspect, the at least one processor may be configured to end the discharging when any of the following first end condition and second end condition is satisfied. The first end condition may be satisfied when voltages of all the cells included in the assembled battery reach the discharging end voltage, and the second end condition may be satisfied when a determination is made that the assembled battery becomes unable to supply the power required for the start processing to the motor when the discharging is continued. When the discharging is ended by the satisfaction of the first end condition, the at least one processor may estimate the deterioration degree of the assembled battery using voltage data of all the cells included in the assembled battery. When the discharging is ended by the satisfaction of the second end condition, the at least one processor may estimate the deterioration degree of the assembled battery using voltage data of a cell of which a voltage reaches the discharging end voltage before the end of the discharging. 
     In the deterioration diagnosis apparatus of the assembled battery, when the discharging is ended by the satisfaction of the first end condition, it is possible to estimate, with high accuracy, the deterioration degree of the assembled battery using the voltage data of all the cells included in the assembled battery. Further, when the second end condition is satisfied, the discharging is ended even when a voltage of any cell included in the assembled battery does not reach the discharging end voltage. As such, the case where the assembled battery becomes unable to supply the power required for the start processing of the internal combustion engine to the motor is restricted from occurring. Therefore, when the discharging is ended by the satisfaction of the second end condition, it is possible to estimate the deterioration degree of the assembled battery using the voltage data of the cell of which the voltage reaches the discharging end voltage before the end of the discharging. 
     A life of the assembled battery is often decided by a deterioration degree of a secondary battery (hereinafter, also referred to as a “minimum capacity cell”) having the smallest full charge capacity from among the cells included in the assembled battery. Then, when the second end condition is satisfied, it is highly possible that a voltage of the minimum capacity cell has already reached the discharging end voltage. For this reason, when the discharging is ended by the satisfaction of the second end condition, it is also considered that the life of the assembled battery can be determined with sufficient accuracy. 
     In the first aspect, the at least one processor may be configured to end the discharging even when the following third end condition is satisfied. The third end condition may be satisfied when a voltage of any cell included in the assembled battery reaches a predetermined voltage. The predetermined voltage may be lower than the discharging end voltage. 
     With the above configuration, at least one of deterioration and abnormality in the cell is restricted. The predetermined voltage may be set based on a discharging prohibition voltage (a lower limit voltage indicating that an abnormality may occur in the cell when the discharging is continued more than the lower limit voltage) common to the cells included in the assembled battery. The predetermined voltage may be set to match the discharging prohibition voltage, or may be set to be slightly higher than the discharging prohibition voltage. Further, the discharging end voltage may be set based on the discharging lower limit voltage (a lower limit voltage indicating that the deterioration of the cell may be accelerated when the discharging is continued more than the lower limit voltage) common to the cells included in the assembled battery. The discharging end voltage may be set to match the discharging lower limit voltage, or may be set to be slightly higher than the discharging lower limit voltage. 
     In the first aspect, the at least one processor may be configured to estimate a full charge capacity of each of the cells using the voltage data indicating a transition of a cell voltage from the discharging start voltage to the discharging end voltage, and classify the cells based on the estimated full charge capacity. 
     The full charge capacity of the cell decreases as the cell deteriorates. With the above configuration, it is easy to grasp a deterioration degree of each cell. 
     In the first aspect, the at least one processor may be configured to, based on the estimated full charge capacity, classify the cells into any of a first category, a second category having a larger full charge capacity than the first category, and a third category having a larger full charge capacity than the second category. Then, the at least one processor may determine that the assembled battery is new when all the cells of which the voltages reach the discharging end voltage before the end of the discharging are classified into the third category. The at least one processor may determine that use of the assembled battery in the vehicle is not continuable when at least one of the cells of which the voltages reach the discharging end voltage before the end of the discharging is classified into the first category. 
     With the above configuration, it is possible to determine whether a state of the assembled battery is any of a new state where the assembled battery is new, a state where the use of the assembled battery is continuable (replacement is not required), or a state where the use thereof is not continuable (replacement is required). As such, it is easy to easily and accurately grasp the deterioration degree of the assembled battery. 
     In the first aspect, the assembled battery may be configured to supply power to a power load mounted on a vehicle. The at least one processor may be configured to execute the discharging by controlling the power load. 
     With the above configuration, it is possible to easily and appropriately execute the deterioration diagnosis of the assembled battery for the vehicle. The power load controlled by the at least one processor during the discharging may include at least one of air conditioning equipment, a seat heater, and a lighting device. 
     In the first aspect, all the cells included in the assembled battery may be connected in series. The at least one processor may be configured to maintain a current value during the discharging of each of the cells. 
     With the above configuration, it is easy to match the current value during the discharging of each cell included in the assembled battery. As such, it is easy to estimate, with high accuracy, the deterioration degree of the assembled battery. 
     A deterioration diagnosis method of an assembled battery according to a second aspect of the present disclosure includes executing discharging of each of a plurality of cells included in the assembled battery while measuring a voltage of each of the cells, repeatedly determining, during the discharging of each of the cells, whether the assembled battery becomes unable to supply power required for start processing to a motor when the discharging is continued, ending the discharging upon determining, during the discharging of each of the cells, that the assembled battery becomes unable to supply the power required for the start processing to the motor when the discharging is continued, and estimating, after the end of the discharging, a deterioration degree of the assembled battery using voltage data, which is acquired during the discharging, of at least one of the cells. The deterioration diagnosis method is executed in a vehicle including an internal combustion engine, a motor that executes start processing of the internal combustion engine, and the assembled battery that supplies power to the motor. 
     In the same manner as the above-described deterioration diagnosis apparatus, with the deterioration diagnosis method of the assembled battery, it is possible to easily execute the start processing of the internal combustion engine after the discharging for the deterioration diagnosis of the assembled battery is executed. 
     In the second aspect, the deterioration diagnosis method may further include determining, using the estimated deterioration degree of the assembled battery, whether use of the assembled battery in the vehicle is continuable, executing, by the motor, the start processing of the internal combustion engine upon determining that the use of the assembled battery in the vehicle is continuable, and charging the assembled battery with power that is generated using drive power output from the started internal combustion engine. 
     With the above configuration, it is possible to easily charge the assembled battery that is discharged for the deterioration diagnosis. 
     A full charge capacity of the assembled battery in an initial state may be 5 kWh or smaller. When the capacity of the assembled battery is 5 kWh or smaller, the diagnosis with the sufficient throughput can be executed using the above-described deterioration diagnosis method due to the discharging. A full charge capacity of the assembled battery to be diagnosed in the initial state may be 0.1 kWh or larger and 5 kWh or smaller, or may be 0.3 kWh or larger and 3 kWh or smaller. The assembled battery to be diagnosed may be a drive battery mounted on a hybrid electric vehicle (HEV). 
     Hereinafter, the internal combustion engine mounted on the vehicle may be referred to as an “engine”. The engine may be configured to generate a traveling driving power. The vehicle may further include a motor that receives power supplied from the assembled battery and generates the traveling driving power, apart from the motor that executes the start processing of the engine. The motor that executes the start processing of the engine may be configured to generate power using drive power that is output from the engine and supply the generated power to the assembled battery. 
     With each aspect of the present disclosure, it is possible to provide a deterioration diagnosis apparatus and a deterioration diagnosis method of an assembled battery that can easily execute start processing of an engine after discharging for the deterioration diagnosis of the assembled battery is executed in a vehicle including an internal combustion engine, a motor that executes the start processing of the internal combustion engine, and an assembled battery that supplies power to the motor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Features, advantages, and technical and industrial significance of exemplary embodiments will be described below with reference to the accompanying drawings, in which like signs denote like elements, and wherein: 
         FIG.  1    is a diagram illustrating a configuration of a vehicle according to an embodiment of the present disclosure; 
         FIG.  2    is a diagram illustrating a configuration of a deterioration diagnosis apparatus of an assembled battery according to the embodiment of the present disclosure; 
         FIG.  3    is a flowchart illustrating a discharging control in a deterioration diagnosis method of the assembled battery according to the embodiment of the present disclosure; 
         FIG.  4    is a graph illustrating an example of discharging characteristics of cells included in the assembled battery illustrated in  FIG.  2   ; 
         FIG.  5    is a graph for describing a method of deciding a discharging end voltage and a first stop voltage in the deterioration diagnosis method of the assembled battery according to the embodiment of the present disclosure; 
         FIG.  6    is a first graph for describing a method of deciding a second stop voltage in the deterioration diagnosis method of the assembled battery according to the embodiment of the present disclosure; 
         FIG.  7    is a second graph for describing the method of deciding the second stop voltage in the deterioration diagnosis method of the assembled battery according to the embodiment of the present disclosure; 
         FIG.  8    is a flowchart illustrating processes executed by a service tool after execution of processes illustrated in  FIG.  3   ; 
         FIG.  9    is a flowchart illustrating details of the processes regarding cell classification illustrated in  FIG.  8   ; 
         FIG.  10    is a diagram for describing a determination of a battery life in the deterioration diagnosis method of the assembled battery according to the embodiment of the present disclosure; 
         FIG.  11    is a flowchart illustrating processes executed by the vehicle after execution of the processes illustrated in  FIG.  8   ; 
         FIG.  12    is a diagram illustrating a modified example of an HVECU illustrated in  FIG.  2   ; and 
         FIG.  13    is a diagram illustrating a modified example of the assembled battery illustrated in  FIG.  2   . 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Embodiments of the present disclosure will be described in detail with reference to drawings. In the drawings, the same or corresponding parts are denoted by the same reference signs and the description thereof will not be repeated. Hereinafter, an electronic control unit is also referred to as an “ECU”. 
       FIG.  1    is a diagram illustrating a configuration of a vehicle according to an embodiment. With reference to  FIG.  1   , a vehicle  100  is a hybrid electric vehicle (HEV). In this embodiment, it is assumed that the vehicle is a front-wheel drive four-wheel vehicle (more specifically, an HEV), but the number of wheels and a drive system can be appropriately changed. For example, the drive system may be four-wheel drive. 
     The vehicle  100  includes a drive battery  11 , a voltage sensor  12   a,  a current sensor  12   b,  a temperature sensor  12   c,  a system main relay (SMR)  14 , a first motor generator  21   a  (hereinafter, referred to as an “MG  21   a ”), a second motor generator  21   b  (hereinafter, referred to as an “MG  21   b ”), a power control unit (PCU)  24 , an engine  31 , a transmission mechanism  421 , and a hydraulic pressure circuit  422 . 
     The drive battery  11  includes a rechargeable secondary battery. The drive battery  11  is configured to supply power to the PCU  24  (and thus the MGs  21   a,    21   b ). In this embodiment, an assembled battery including a plurality of secondary batteries that are electrically connected to each other is employed as the drive battery  11 . A full charge capacity of the drive battery  11  in an initial state may be, for example, approximately 1.5 kWh. The secondary batteries included in the drive battery  11  may be modularized by a predetermined number. The assembled battery may be composed by combining a plurality of modules. The number of secondary batteries included in the drive battery  11  may be 10 or more and less than 100, or may be 100 or more. In this embodiment, the number of secondary batteries included in the drive battery  11  is approximately 50. The drive battery  11  is assembled in a form of a battery pack on, for example, a floor panel of the vehicle  100 . In this embodiment, the battery pack is formed by installing accessories (a voltage sensor  12   a,  a current sensor  12   b,  a temperature sensor  12   c,  a battery ECU  13 , an SMR  14 , and the like) in a battery case that accommodates the drive battery  11 . 
     Each secondary battery included in the assembled battery is referred to as a “cell”. In this embodiment, all the cells included in the assembled battery are connected in series (see, for example,  FIG.  2    described below). In this embodiment, a liquid system lithium-ion secondary battery is employed as a cell. However, examples of the cell are not limited thereto, and an all-solid-state secondary battery may be employed as a cell. Further, examples of the cell are not limited to the lithium-ion secondary battery, and may include other secondary batteries (for example, a nickel-hydrogen battery). Examples of the form of assembling the drive battery  11  in the vehicle  100  are not limited to the battery pack, and may include a packless form. 
     The voltage sensor  12   a  detects a voltage of each cell of the drive battery  11 . The current sensor  12   b  detects current flowing through the drive battery  11 . The temperature sensor  12   c  detects a temperature of each cell of the drive battery  11 . Each sensor outputs a detection result to the battery ECU  13 . The battery ECU  13  calculates a State of Charge (SOC) of each cell and an SOC of the drive battery  11  using the detection result of each sensor. The SOC indicates a remaining accumulated power amount and represents a ratio of, for example, a current accumulated power amount to an accumulated power amount in a fully charged state from 0% to 100%. The current sensor  12   b  is provided in a current path of the drive battery  11 . In this embodiment, one voltage sensor  12   a  and one temperature sensor  12   c  are provided to each cell. 
     The SMR  14  is configured to switch between connection/disconnection of the current path that connects the PCU  24  to the drive battery  11 . As the SMR  14 , for example, an electromagnetic mechanical relay can be employed. When the SMR  14  is in a closed state (a connected state), power can be sent and received between the drive battery  11  and the PCU  24 . On the other hand, when the SMR  14  is in an open state (a disconnected state), the current path that connects the drive battery  11  to the PCU  24  is disconnected. The SMR  14  is controlled by an HVECU  50 . The SMR  14  is switched to the closed state when, for example, the vehicle  100  is traveling. 
     Each of the MGs  21   a  and  21   b  is a motor generator that has both a function as a motor that outputs torque by receiving supply of driving power and a function as a generator that generates generated power by receiving torque. As each of the MGs  21   a  and  21   b,  an alternating current motor (for example, a permanent magnet type synchronous motor or an induction motor) is used. Each of the MGs  21   a  and  21   b  is electrically connected to the drive battery  11  via the PCU  24 . The MGs  21   a,    21   b  have rotor shafts  43   a,    43   b , respectively. The rotor shafts  43   a,    43   b  correspond to rotation shafts of the MGs  21   a,    21   b , respectively. 
     The vehicle  100  further includes a single pinion type planetary gear  431 . An output shaft  41  of the engine  31  is connected to the planetary gear  431  through the transmission mechanism  421 . As the engine  31 , any internal combustion engine can be employed, but in this embodiment, as the engine  31 , a spark-ignition type internal combustion engine including a plurality of cylinders (for example, four cylinders) is employed. The engine  31  generates drive power by combusting fuel (for example, gasoline) in each cylinder, and rotates a crankshaft (not shown) common to all cylinders using the generated drive power. The crankshaft of the engine  31  is connected to the output shaft  41  via a torsional damper (not shown). As the crankshaft rotates, the output shaft  41  also rotates. An example of the engine  31  is not limited to a gasoline engine, and may include a diesel engine or a hydrogen engine. 
     The output shaft  41  of the engine  31  corresponds to an input shaft of the transmission mechanism  421 . The transmission mechanism  421  includes a clutch and a brake (neither shown), and is configured to change a gear ratio (that is, a ratio of rotation speed of the input shaft of the transmission mechanism  421  to rotation speed of an output shaft  42  of the transmission mechanism  421 ) depending on states (engagement/disengagement) of the clutch and the brake. The hydraulic pressure circuit  422  is configured to adjust hydraulic pressure supplied to each of the clutch and the brake included in the transmission mechanism  421  according to a command from the HVECU  50 . The HVECU  50  may switch the state (engagement/disengagement) of each of the clutch and the brake included in the transmission mechanism  421  by controlling the hydraulic pressure circuit  422 . In the configuration illustrated in  FIG.  1   , the transmission mechanism  421  is positioned on the upstream side (the planetary gear  431 ) of a power split device, but the transmission mechanism  421  may be positioned on the downstream side (the side close to drive wheels  45   a,    45   b ). 
     The vehicle  100  further includes a shift lever  101  and a P position switch  102 . Each of the shift lever  101  and the P position switch  102  is configured to be able to switch between a plurality of shift ranges according to a shift operation of a user. The user can select any of a neutral (N) range, a reverse (R) range, a drive (D) range, and a brake (B) range by moving the shift lever  101  to a predetermined position. Further, the user can select a parking (P) range by stopping the vehicle  100  and pressing the P position switch  102 . The HVECU  50  switches the shift range of the vehicle  100  to a range selected by the user. The HVECU  50  controls the hydraulic pressure circuit  422  according to, for example, the shift range. 
     Each of the output shaft  42  of the transmission mechanism  421  and the rotor shaft  43   a  of the MG  21   a  is connected to the planetary gear  431 . The planetary gear  431  has three rotating elements, that is, an input element, an output element, and a reaction force element. More specifically, the planetary gear  431  has a sun gear, a ring gear coaxially arranged with the sun gear, a pinion gear that meshes with the sun gear and the ring gear, and a carrier that holds the pinion gear such that it can rotate and revolve. The carrier corresponds to the input element, the ring gear corresponds to the output element, and the sun gear corresponds to the reaction force element. 
     The output shaft  42  of the transmission mechanism  421  is connected to the carrier of the planetary gear  431 . The rotor shaft  43   a  of the MG  21   a  is connected to the sun gear of the planetary gear  431 . Torque is input from the output shaft  42  of the transmission mechanism  421  to the carrier of the planetary gear  431 . The planetary gear  431  is configured to, when the transmission mechanism  421  is in a non-neutral state (that is, a state of transferring the drive power), divide and transfer the torque output by the engine  31  to the sun gear (and thus the MG  21   a ) and the ring gear. When the torque output by the engine  31  is output to the ring gear, a reaction force torque output by the MG  21   a  acts on the sun gear. 
     The planetary gear  431  and the MG  21   b  are configured to combine drive power output from the planetary gear  431  (that is, drive power output to the ring gear) and drive power output from the MG  21   b  (that is, drive power output to the rotor shaft  43   b ) and transfer the combined power to drive wheels  45   a,    45   b.  More specifically, an output gear (not shown) that meshes with a driven gear  432  is installed at the ring gear of the planetary gear  431 . Further, a drive gear (not shown) installed at the rotor shaft  43   b  of the MG  21   b  also meshes with the driven gear  432 . The driven gear  432  acts to combine torque output by the MG  21   b  to the rotor shaft  43   b  with torque output from the ring gear of the planetary gear  431 . The drive torque combined as above is transferred to a differential gear  44 , and further transferred to the drive wheels  45   a,    45   b  via the drive shafts  44   a,    44   b  extending to the right and left from the differential gear  44 . 
     The vehicle  100  further includes a battery ECU  13 , a motor ECU  23 , an engine ECU  33 , and an HVECU  50 . In this embodiment, a computer (for example, a microcomputer) is employed as each of the battery ECU  13 , the motor ECU  23 , the engine ECU  33 , and the HVECU  50 . The ECUs are connected to each other in a manner capable of executing CAN communication therebetween. 
     The HVECU  50  includes a processor  51 , a random access memory (RAM)  52 , and a storage device  53 . As the processor  51 , for example, a central processing unit (CPU) can be employed. The RAM  52  functions as a working memory that temporarily stores data processed by the processor  51 . The storage device  53  is configured to be able to retain the stored information. In addition to the program, the storage device  53  stores information (for example, a map, a mathematical formula, and various parameters) used in the program. When the processor  51  executes the program stored in the storage device  53 , various processes are executed in the HVECU  50 . 
     Although  FIG.  1    illustrates a detailed configuration of only the HVECU  50 , each of the other ECUs also includes a processor, a RAM, and a storage device. The number of processors included in each ECU is arbitrary, and any ECU may include a plurality of processors. Further, various processes in each ECU are not limited to execution by software, and may be executed by dedicated hardware (an electronic circuit). 
     Motor sensors  22   a,    22   b  that detect states (for example, current, a voltage, a temperature, and rotation speed) of the MGs  21   a,    21   b  are provided in the MGs  21   a,    21   b , respectively. Each of the motor sensors  22   a,    22   b  outputs a detection result to the motor ECU  23 . An engine sensor  32  that detects a state (for example, an air intake amount, air intake pressure, an air intake temperature, exhaust pressure, an exhaust temperature, a catalyst temperature, an engine coolant temperature, and rotation speed) of the engine  31  is provided in the engine  31 . The engine sensor  32  outputs a detection result to the engine ECU  33 . The HVECU  50  receives detection values of the motor sensors  22   a,    22   b  and the engine sensor  32  from the motor ECU  23  and the engine ECU  33 , as necessary. Further, the HVECU  50  receives a state (for example, a cell voltage, current, and a temperature, and the SOC) of the drive battery  11  from the battery ECU  13 , as necessary. 
     The vehicle  100  includes a monitoring unit  80   a  that detects a state of an auxiliary battery  80  described below. The monitoring unit  80   a  includes various sensors that detect a state (for example, a temperature, current, a voltage) of the auxiliary battery  80 , and outputs a detection result to the HVECU  50 . The HVECU  50  can acquire the state (for example, the temperature, current, the voltage, and an SOC) of the auxiliary battery  80  based on an output of the monitoring unit  80   a.  Further, although not shown, other sensors (for example, a vehicle speed sensor, a fuel gauge, an odometer, an accelerator operation amount sensor, and an atmospheric pressure sensor) that indicate a situation of the vehicle  100  are also mounted on the vehicle  100 . The HVECU  50  can grasp information of the vehicle  100  based on outputs of various sensors (in-vehicle sensors) mounted on the vehicle  100 . 
     The HVECU  50  is configured to output a command (a control command) for controlling the engine  31  to the engine ECU  33 . The engine ECU  33  is configured to control various actuators (for example, a throttle valve, an ignition device, and an injector) (none of them shown) of the engine  31  according to the command from the HVECU  50 . The HVECU  50  can control the engine through the engine ECU  33 . 
     The HVECU  50  is configured to output a command (a control command) for controlling each of the MG  21   a  and the MG  21   b  to the motor ECU  23 . The motor ECU  23  is configured to generate a current signal (for example, a signal indicating a magnitude and frequency of current) corresponding to a target torque of each of the MG  21   a  and the MG  21   b  according to the command from the HVECU  50 , and to output the generated current signal to the PCU  24 . The HVECU  50  can control the motors through the motor ECU  23 . 
     The PCU  24  includes, for example, two inverters (not shown) provided to correspond to the MGs  21   a,    21   b,  and a converter (not shown) arranged between each inverter and the drive battery  11 . The PCU  24  is configured to supply power accumulated in the drive battery  11  to each of the MG  21   a  and the MG  21   b,  and to supply power generated by each of the MG  21   a  and the MG  21   b  to the drive battery  11 . The PCU  24  is configured to be able to separately control the states of the MGs  21   a,    21   b,  that is, for example, it can turn the MG  21   b  to a power running state while turning the MG  21   a  to a power generation state. 
     The MG  21   a  is configured to execute start processing of the engine  31 . Specifically, when the engine  31  is started, the MG  21   a  that receives power supplied from the drive battery  11  executes cranking of the engine  31 . 
     The MG  21   a  is configured to generate power (that is, engine power generation) using drive power output from the engine  31 . The HVECU  50  charges the drive battery  11  with power generated by the engine power generation such that the SOC of the drive battery  11  does not become excessively low while the vehicle  100  is traveling. Further, the drive battery  11  is also charged with power generated by regenerative braking by the MG  21   b.    
     The vehicle  100  is configured to execute HV traveling and EV traveling. The HV traveling is executed by the engine  31  and the MG  21   b  while the engine  31  is generating traveling driving power. The EV traveling is executed by the MG  21   b  when the engine  31  is in a stopped state. When the engine  31  is in the stopped state, combustion in each cylinder is not executed. When the combustion in each cylinder is stopped, combustion energy (and thus traveling driving power) is not generated in the engine  31 . 
     The vehicle  100  further includes an auxiliary battery  80 , DC/DC converters  81 ,  82 , an auxiliary relay  83 , a high voltage load  91 , and a low voltage load  92 . The full charge capacity of the auxiliary battery  80  is smaller than that of the drive battery  11 . A full charge capacity of a battery is an electricity amount accumulated in the battery in a fully charged state and decreases as the battery deteriorates. As the auxiliary battery  80 , for example, a lead battery can be employed. However, as the auxiliary battery  80 , a secondary battery (for example, a nickel-hydrogen battery) other than the lead battery may be employed. The DC/DC converters  81 ,  82 , the auxiliary relay  83 , the high voltage load  91 , and the low voltage load  92  are controlled by the HVECU  50 . The HVECU  50  may control these through the battery ECU  13 . 
     The high voltage load  91  is an auxiliary machine of a high voltage system. The low voltage load  92  is an auxiliary machine of a low voltage system. A drive voltage of the low voltage load  92  is lower than a drive voltage of the high voltage load  91 . The auxiliary battery  80  is an in-vehicle battery of the low voltage system (for example, a 12 V system), and is configured to supply power to the low voltage load  92 . In this embodiment, the high voltage load  91  includes air conditioning equipment and the low voltage load  92  includes a lighting device. The air conditioning equipment is configured to heat and cool a cabin of the vehicle  100 . The lighting device includes a lighting device that illuminates the inside of the vehicle and a lighting device (for example, a headlight) that illuminates the outside of the vehicle. At least one of the high voltage load  91  and the low voltage load  92  may further include a seat heater that heats a seat of the vehicle  100 . 
     The DC/DC converter  81  is provided between the drive battery  11  and the high voltage load  91 , steps down power supplied from the drive battery  11  and outputs it to the high voltage load  91 . The DC/DC converter  82  steps down power supplied from the drive battery  11  and outputs it to each of the auxiliary battery  80  and the low voltage load  92 . When the SMR  14  is in the open state (the disconnected state), power of the drive battery  11  is not supplied to any of the high voltage load  91 , the low voltage load  92 , and the auxiliary battery  80 . An auxiliary relay  83  is arranged in a current path that connects the DC/DC converter  82  to the low voltage load  92 . When the auxiliary relay  83  is in the open state (the disconnected state), power is not supplied to the low voltage load  92 . 
     When the SMR  14  is in the closed state (the connected state), power can be supplied from the drive battery  11  to the auxiliary battery  80  through the DC/DC converter  82 . For example, when the SOC of the auxiliary battery  80  is lower than a predetermined value, the HVECU  50  charges the auxiliary battery  80  with power of the drive battery  11 . Further, the HVECU  50  drives the high voltage load  91  and the low voltage load  92  using power of the drive battery  11  according to an instruction from a service tool  200  (see  FIG.  2   ) in the deterioration diagnosis (see S 16  of  FIG.  3   ) of the assembled battery described below. At this time, the HVECU  50  controls the SMR  14 , the DC/DC converters  81 ,  82 , and the auxiliary relay  83  such that power of the drive battery  11  is supplied to each of the high voltage load  91  and the low voltage load  92 . 
     The HVECU  50  is configured to execute an SOC limit control to the drive battery  11 . The SOC limit control is a control for limiting the SOC of the drive battery  11  to within a predetermined SOC range. The HVECU  50  limits an input/output of the drive battery  11  such that the SOC of the drive battery  11  does not leave the SOC range. Specifically, the HVECU  50  controls the MGs  21   a,    21   b,  the engine  31 , and the DC/DC converters  81 ,  82  such that the SOC of the drive battery  11  is within the SOC range. The SOC range is variably set depending on a state of the vehicle  100 . The HVECU  50  may set an SOC range for protecting the drive battery  11  and its peripheral parts using, for example, a map stored in the storage device  53 . 
     The vehicle  100  further includes a power switch  103 . The power switch  103  is used for switching between start/stop of a vehicle system (the HVECU  50  and the like). The power switch  103  is operated by the user. 
     The vehicle  100  further includes a notification device  104 . The notification device  104  is configured to send a notification to the user of the vehicle  100  in response to a request from the HVECU  50 . Examples of the notification device  104  can include a meter panel, a head-up display, a navigation display, a warning light, or a speaker. The notification device  104  may function as an input device that receives an input from the user. The notification device  104  may include a touch panel display or a smart speaker that receives a voice input. The notification device  104  may be mounted on a portable device (that is, an electronic device that can be carried by the user), such as a tablet terminal, a smartphone, or a wearable device. 
       FIG.  2    is a diagram illustrating a configuration of a deterioration diagnosis apparatus of an assembled battery according to this embodiment. With reference to  FIG.  2    together with  FIG.  1   , in this embodiment, the service tool  200  functions as a deterioration diagnosis apparatus of an assembled battery. The service tool  200  includes a computer including a processor  201 , a RAM  202 , and a storage device  203 . The storage device  203  stores a diagnosis program. A deterioration diagnosis method (see  FIGS.  3 ,  8 , and  9    described below) of an assembled battery according to this embodiment is executed when the processor  201  executes the diagnosis program stored in the storage device  203 . 
     The service tool  200  further includes a human machine interface (HMI)  204 . The HMI  204  includes an input device and a display device. The HMI  204  may be a touch panel display. The HMI  204  may include a smart speaker that receives a voice input. 
     The HVECU  50  further includes a data link connector (DLC)  55   a  and an interface  55   b  of the DLC  55   a.  The DLC  55   a  is a connector that can be connected to a connector  250  of the service tool  200 , and is arranged in, for example, the vicinity of a driver seat of the vehicle  100 . The service tool  200  is an external diagnosis machine used by, for example, a worker (such as a mechanic) in a maintenance shop to grasp a state of a vehicle. Examples of the service tool  200  can include a general scan tool (GST). By connecting the connector  250  of the service tool  200  to the DLC  55   a,  the service tool  200  can read vehicle data stored in the storage device  53 . 
     In the deterioration diagnosis method of the assembled battery according to this embodiment, the service tool  200  discharges each cell included in the drive battery  11  (the assembled battery) while measuring a voltage of each cell. The service tool  200  ends the discharging when the first end condition is satisfied. The first end condition is satisfied when the voltages of all the cells included in the drive battery  11  have reached a predetermined discharging end voltage (hereinafter, referred to as “V end1 ”). After the end of the discharging, the service tool  200  estimates the deterioration degree of the drive battery  11  using voltage data indicating a transition of a voltage of at least one cell included in the drive battery  11  from the discharging start voltage to V end1 . 
     However, when a discharging end timing is decided only by the first end condition, the discharging of the drive battery  11  may be continued even when the drive battery  11  becomes unable to supply power required for the start processing of the engine  31  to the MG  21   a.  In such a diagnosis method, it may take time and effort to charge the drive battery  11  with an external power source (a power source outside the vehicle) after the end of the diagnosis. 
     Therefore, in the deterioration diagnosis method of the assembled battery according to this embodiment, the discharging is ended not only when the first end condition is satisfied but also when the second or third end condition described below is satisfied. In more detail, the service tool  200  determines, during the discharging of the drive battery  11 , whether the drive battery  11  becomes unable to supply the power required for the start processing of the engine  31  to the MG  21   a  when the discharging is continued. Then, when it is determined that the drive battery  11  becomes unable to supply the power required for the start processing of the engine  31  to the MG  21   a  when the discharging is continued, the second end condition is satisfied. Then, the service tool  200  ends the discharging when the second end condition is satisfied. As such, the discharging of the drive battery  11  is ended before the drive battery  11  becomes unable to supply the power required for the start processing of the engine  31  to the MG  21   a.  For this reason, the MG  21   a  can receive power supplied from the drive battery  11  after the end of the discharging and execute the start processing of the engine  31 . With the deterioration diagnosis method of the assembled battery according to this embodiment, it is possible to easily execute the start processing of the engine  31  after the discharging for the deterioration diagnosis of the drive battery  11  is executed. 
     The service tool  200  according to this embodiment includes a discharging unit  211  and an estimation unit  212 . The discharging unit  211  is configured to discharge each cell while measuring the voltage of each cell included in the drive battery  11  mounted on the vehicle  100 . The estimation unit  212  is configured to estimate the deterioration degree of the drive battery  11  using the acquired voltage data indicating the transition of the voltage of at least one cell included in the drive battery  11  from the discharging start voltage to V end1 . The discharging unit  211  is configured to determine, during the discharging of each cell included in the drive battery  11 , whether the drive battery  11  becomes unable to supply the power required for the start processing of the engine  31  to the MG  21   a  when the discharging is continued, and to end the discharging before the drive battery  11  becomes unable to supply the power required for the start processing of the engine  31  to the MG  21   a.    
       FIG.  3    is a flowchart illustrating discharging control in the deterioration diagnosis method of the assembled battery according to this embodiment. Processes illustrated in this flowchart are executed when, for example, a predetermined instruction is input from the user to the HMI  204  after the connector  250  of the service tool  200  is connected to the DLC  55   a  of the vehicle  100  in a parked state. However, a condition of starting the process illustrated in  FIG.  3    is not limited thereto, and can be arbitrarily set. The discharging unit  211  of the service tool  200  transmits a control command to the HVECU  50 , whereby each step of  FIG.  3    is executed. Hereinafter, each step in the flowchart is simply referred to as “S”. 
     With reference to  FIG.  3    together with  FIGS.  1  and  2   , in S 10 , the service tool  200  releases the SOC range regarding the SOC limit control. As such, the SOC limit (the SOC limit control) of the drive battery  11  becomes invalid. 
     Subsequently in S 11 , the service tool  200  drives the engine  31  and charges the drive battery  11  with power generated by the engine power generation. By the process of S 11 , power generated by the MG  21   a  using drive power output from the engine  31  is input to the drive battery  11  via the PCU  24  and the SMR  14 . 
     In S 12 , the service tool  200  determines whether the voltages of all the cells included in the drive battery  11  have become a predetermined start voltage (hereinafter, referred to as “V start ”) or higher. The voltage of each cell included in the drive battery  11  is measured by the voltage sensor  12   a.  V start  may be a cell voltage indicating that the cell has turned to the fully charged state, or may be a charging upper limit voltage of the cell. The charging upper limit voltage corresponds to an upper limit value of a recommended voltage range. When the charging of the cell is continued until the voltage exceeds the charging upper limit voltage, the cell may be over-charged. The over-charging accelerates the deterioration of the cell. V start  may be 3.6 V or higher and 3.9 V or lower, or may be approximately 3.6 V. Further, the service tool  200  may determine whether the voltages of all the cells included in the drive battery  11  have become V start  or higher based on the SOC of the drive battery  11 . For example, when the SOC of the drive battery  11  has become a predetermined SOC value (for example, 70%) or higher, the service tool  200  may determine that the voltages of all the cells included in the drive battery  11  have become V start  or higher. 
     The processes of S 11  and S 12  are repeated until the voltages of all the cells included in the drive battery  11  become V start  or higher (NO in S 12 ). When the voltages of all the cells become V start  or higher (YES in S 12 ), in S 13 , the service tool  200  stops the engine  31 . Thereafter, in S 14 , the service tool  200  determines whether the voltages of all the cells included in the drive battery  11  have become stable. The process stands by in S 14  until the voltage of each cell included in the drive battery  11  becomes stable, and, when the voltage of each cell included in the drive battery  11  becomes stable (YES in S 14 ), the process proceeds to S 15 . 
     In S 15 , the service tool  200  measures a state (a voltage, current, and a temperature) of each cell included in the drive battery  11 , and records a measurement result in the storage device  203 . Subsequently in S 16 , the service tool  200  discharges the drive battery  11  by controlling a power load of the vehicle  100 . The drive battery  11  is configured to supply power to the power load mounted on the vehicle  100 . 
     Specifically, in S 16 , the service tool  200  controls the power load (for example, at least one of the high voltage load  91  and the low voltage load  92 ) of the vehicle  100  such that discharging current of each cell included in the drive battery  11  becomes a predetermined value (hereinafter, referred to as “Vd”). In this embodiment, the air conditioning equipment (the high voltage load  91 ) and the lighting device (the low voltage load  92 ) are driven by power supplied from the drive battery  11 . The service tool  200  adjusts power supplied from the drive battery  11  to the high voltage load  91  and the low voltage load  92 , using the DC/DC converters  81 ,  82 , respectively. Then, the service tool  200  maintains a current value during the discharging of each cell included in the drive battery  11 . Vd may be 1 A or higher and 10 A or lower, or may be approximately 5 A. In this embodiment, the current value during the discharging of each cell is maintained at Vd. In this embodiment, Vd is set to a fixed value (for example, 5 A), but Vd may be variable depending on the situation. 
     In S 17 , the service tool  200  determines whether the first end condition is satisfied. Specifically, the service tool  200  determines whether the voltages of all the cells included in the drive battery  11  have reached the predetermined discharging end voltage (V end1 ). 
       FIG.  4    is a graph illustrating an example of discharging characteristics of the cells included in the drive battery  11 . With reference to  FIG.  4   , when the discharging of the cell is started, the cell voltage gradually decreases. A decrease amount of a cell voltage per unit discharging amount (corresponding to a slope of the graph) is substantially constant immediately after the start of the discharging, but increases for a while when the discharging is continued. Then, when the discharging is further continued, the cell voltage reaches V end1 .  FIG.  4    illustrates the transition of the voltage of one cell, but the transition of the voltage during the discharging is different for each cell. 
     With reference to  FIG.  3    together with  FIGS.  1  and  2    again, when a voltage of any cell included in the drive battery  11  does not reach V end1  (NO in S 17 ), the process proceeds to S 18 . In S 18 , the service tool  200  determines whether the third end condition is satisfied. The third end condition is satisfied when a voltage of any cell included in the drive battery  11  has reached a predetermined first stop voltage (hereinafter, referred to as “V end3 ”). 
       FIG.  5    is a graph for describing a method of deciding the discharging end voltage (V end1 ) and the first stop voltage (V end3 ) in the deterioration diagnosis method of the assembled battery according to this embodiment. Lines L 1  to L 3  in  FIG.  5    respectively illustrate examples of a transition of current and voltages of the drive battery  11  (the assembled battery) when S 10  to S 16  of  FIG.  3    are executed, and the discharging (S 16 ) is continued for a predetermined time. The line L 1  illustrates a transition of current of the drive battery  11 . Lines L 2  and L 3  respectively illustrate the discharging characteristics (more specifically, the transitions of the cell voltages during the discharging) of a first cell and a second cell included in the drive battery  11 . A full charge capacity of the first cell is larger than that of the second cell. 
     With reference to  FIG.  5   , in a comparison between the transition of a voltage of the first cell (the line L 2 ) and the transition of a voltage of the second cell (the line L 3 ), the voltage of the second cell starts to decrease earlier than that of the first cell and decreases to a voltage lower than a voltage to which the voltage of the first cell decreases. As such, the cell voltage tends to easily decrease during the discharging as a full charge capacity is smaller. When the voltage of the cell decreases too much due to the discharging of the cell, the deterioration of the cell is accelerated. The fact that the discharging of the voltage of the cell is continued until it decreases too much is referred to as the “over-discharging”. 
     In the deterioration diagnosis method of the assembled battery according to this embodiment, V end1  is set such that the over-discharging of the cell is restricted. Specifically, V end1  is set based on a discharging lower limit voltage common to all the cells included in the drive battery  11 . The discharging lower limit voltage corresponds to a lower limit value of the recommended voltage range. When the discharging of a cell is continued until its voltage falls below the discharging lower limit voltage, the cell may be over-discharged. In this embodiment, V end1  is set to a voltage slightly higher than the discharging lower limit voltage (for example, a value obtained by adding an extra voltage to the discharging lower limit voltage). V end1  may be 2.8 V or higher and 3.2 V or lower. In this embodiment, V end1  is set to 3.0 V. Then, in the processes illustrated in  FIG.  3   , when the voltages of all the cells included in the drive battery  11  reach V end1  (YES in S 17 ), the discharging of the drive battery  11  is ended (see S 20  described below). 
     When the discharging of the cell is excessively continued after the cell voltage has become lower than the discharging lower limit voltage, an abnormality (for example, malfunction or failure) may occur in the cell. In the deterioration diagnosis method of the assembled battery according to this embodiment, V end3  is set such that an abnormality does not occur in the cell. Specifically, V end3  is set based on a discharging prohibition voltage common to all the cells included in the drive battery  11 . The discharging prohibition voltage corresponds to a dischargeable limit value, and when the discharging of the cell is continued until its voltage falls below the discharging prohibition voltage, an abnormality may occur in the cell. In this embodiment, V end3  is set to a voltage slightly higher than the discharging prohibition voltage (for example, a value obtained by adding an extra voltage to the discharging prohibition voltage). V end3  is a value lower than V end1 . V end3  may be 2.0 V or higher and 2.5 V or lower. In this embodiment, V end3  is set to 2.3 V. Then, in the processes illustrated in  FIG.  3   , when a voltage of any cell included in the drive battery  11  reaches V end3  (YES in S 18 ), the discharging of the drive battery  11  is ended (see S 20  described below). 
     With reference to  FIG.  3    together with  FIGS.  1  and  2    again, when a voltage of any cell included in the drive battery  11  has not reached V end3  (NO in S 18 ), the process proceeds to S 19 . In S 19 , the service tool  200  determines whether the second end condition is satisfied. Specifically, the service tool  200  determines whether engine cranking is not established when the discharging is continued (that is, whether the drive battery  11  becomes unable to supply the power required for the start processing of the engine  31  to the MG  21   a  when the discharging is continued). In this embodiment, at a time at which the average value (hereinafter, also referred to as the “average cell voltage”) of the voltages of all the cells included in the drive battery  11  (the assembled battery) has become a predetermined second stop voltage (hereinafter, referred to as “V end2 ”) or lower, it is determined that the drive battery  11  becomes unable to supply the power required for the start processing of the engine  31  to the MG  21   a  when the discharging is continued after the time. Hereinafter, with reference to  FIGS.  6  and  7   , a method of deciding the second stop voltage (V end2 ) in the deterioration diagnosis method of the assembled battery according to this embodiment will be described. 
       FIG.  6    illustrates a first graph for describing the method of deciding the second stop voltage (V end2 ). A line L 11  in  FIG.  6    illustrates a voltage distribution (hereinafter, referred to as a “first cell voltage distribution”) of all the cells included in a first assembled battery. A line L 12  in  FIG.  6    illustrates a voltage distribution (hereinafter, referred to as a “second cell voltage distribution”) of all the cells included in a second assembled battery. In  FIG.  6   , V ave1  and V ave2  represent the average cell voltages of the first assembled battery and the second assembled battery, respectively. V cr  represents a lower limit voltage for cranking establishment. In each assembled battery, when the average cell voltage falls below V cr , the cranking is not established. 
     The first cell voltage distribution (the line L 11 ) and the second cell voltage distribution (the line L 12 ) illustrated in  FIG.  6    are distributions when the discharging is continued until the first end condition is satisfied for the first assembled battery and the second assembled battery, respectively. In other words, voltages of all the cells included in each of the first and second assembled batteries have become V end1  or lower. 
     With reference to  FIG.  6   , the first cell voltage distribution corresponds to a normal distribution (general variations). The average cell voltage (V ave1 ) of the first assembled battery is higher than V cr . For this reason, the first assembled battery can supply power required for the cranking. On the other hand, in the second cell voltage distribution, the cell voltages are biased toward the low voltage side. The average cell voltage (V ave2 ) of the second assembled battery is lower than V cr . For this reason, the second assembled battery becomes unable to supply power required for the cranking. 
       FIG.  7    illustrates a second graph for describing the method of deciding the second stop voltage (V end2 ). The second cell voltage distribution (a line L 12 ) illustrated in  FIG.  7    is the distribution when the discharging of the second assembled battery is ended at a timing at which the second end condition is satisfied. In other words, the average cell voltage (V ave2 ) of the second assembled battery matches the second stop voltage (V end2 ). In this embodiment, V end2  is set to a voltage (for example, a value obtained by adding an extra voltage to V cr ) slightly higher than V cr . V cr  is a voltage value required for the MG  21   a  to execute the start processing of the engine  31 . 
     In the processes illustrated in  FIG.  3   , at a time at which the average cell voltage of the drive battery  11  becomes V end2  or lower (YES in S 19 ), the discharging of the drive battery  11  is ended (see S 20  described below). When the determination is positive in S 19 , it means that the drive battery  11  becomes unable to supply the power required for the start processing of the engine  31  to the MG  21   a  when the discharging is continued after the time. When the second end condition is satisfied before the first end condition is satisfied, and the discharging is ended, voltages of some cells included in the drive battery  11  (the assembled battery) do not reach V end1  (see  FIG.  7   ). However, since these cells are considered to have a sufficiently large capacity, it is considered that there is no significant influence on the accuracy of determination (see  FIGS.  8  to  10   ) of the life of the assembled battery described below. In this embodiment, V end2  is set to the average cell voltage (the average value of the voltages of all the cells included in the assembled battery), but the median value may be employed instead of the average value. V end2  may be set to the median value of the voltages of all the cells included in the assembled battery. 
     With reference to  FIG.  3    together with  FIGS.  1  and  2    again, while none of the first to third end conditions are satisfied (NO in all of S 17  to S 19 ), the processes of S 15  to S 19  are repeated, and the discharging of the drive battery  11  is continued. Then, when any of the first to third end conditions is satisfied (YES in any of S 17  to S 19 ), in S 20 , the service tool  200  ends the discharging of the drive battery  11 . 
     After ending the discharging of the drive battery  11  in S 20 , the service tool  200  restarts the SOC limit control. As such, the SOC of the drive battery  11  is limited to within the predetermined SOC range, again. Then, when the process of S 20  is executed, a series of processes illustrated in  FIG.  3    ends. 
     By the above-described processes illustrated in  FIG.  3   , the data indicating a state (particularly, the deterioration degree) of the drive battery  11  is recorded in the storage device  203  of the service tool  200 . The service tool  200  estimates the deterioration degree of the drive battery  11  using the recorded data of the drive battery  11 . Then, the service tool  200  determines whether a life of the drive battery  11  has run out (that is, whether the use of drive battery  11  can be continued). 
       FIG.  8    is a flowchart illustrating processes executed by the service tool  200  after the execution of the processes illustrated in  FIG.  3   . The processes illustrated in this flowchart are executed when a predetermined instruction is input from the user to the HMI  204  after the service tool  200  acquires the data of the drive battery  11  by, for example, the processes illustrated in  FIG.  3   . However, a condition for starting the process illustrated in  FIG.  8    is not limited thereto and can be arbitrarily set. For example, the process illustrated in  FIG.  8    may be automatically started after the process illustrated in  FIG.  3    ends. Each step illustrated in  FIG.  8    is executed by the estimation unit  212  of the service tool  200 . In this embodiment, the processes illustrated in  FIG.  8    described below are executed in a state where the vehicle  100  and the service tool  200  are connected to each other. 
     With reference to  FIG.  8    together with  FIGS.  1  and  2   , in S 31 , the service tool  200  estimates the full charge capacity of each cell of which a voltage has reached V end1  due to the above-described discharging (S 16  of  FIG.  3   ) from among all the cells included in the drive battery  11 . When the discharging is ended by the satisfaction of the first end condition (YES in S 17  of  FIG.  3   ), the full charge capacities of all the cells included in the drive battery  11  are estimated. When the discharging is ended by the satisfaction of the second or third end condition (YES in S 18  or S 19  of  FIG.  3   ), a full charge capacity of only a cell of which a voltage has reached V end1  before the end of the discharging is estimated. 
     Specifically, the service tool  200  acquires a section discharging amount (Ah) from the discharging start voltage to V end1  (the discharging end voltage) of each cell using the data (including the voltage data indicating the transition of the cell voltage from the discharging start voltage to the discharging end voltage) acquired in S 15  of  FIG.  3   . The discharging amount corresponds to a time integral value of a discharging current (A). When the discharging current fluctuates within a section, the section discharging amount can be obtained by integrating the discharging current for each unit time with respect to time. When the discharging current is constant within the section, a value obtained by multiplying the discharging current (A) by a discharging period (h) corresponds to the discharging amount. 
     As above, the service tool  200  calculates the section discharging amount (that is, the section discharging amount from the discharging start voltage to V end1 ) of the cell and converts the section discharging amount into the full charge capacity using a predetermined map. A map illustrating a relationship between a temperature of the cell, the section discharging amount, and the full charge capacity may be used to obtain the full charge capacity of the cell. When the temperature of the cell and the section discharging amount are given to the map, the full charge capacity of the cell is output from the map. The temperature of the cell that is used may be the average temperature during the discharging or the temperature at the start of the discharging. The map may be stored in the storage device  203  in advance. The service tool  200  may acquire the map from an external server (for example, a server that manages information on various batteries), or may acquire the map from the vehicle  100 . 
     Subsequently in S 32 , the service tool  200  classifies a cell based on the full charge capacity (hereinafter, also referred to as a “cell estimation capacity”) of the cell that is estimated in S 31 . A target of the classification is a cell of which a full charge capacity has been estimated in S 31 . The classification is executed for each cell. Specifically, the service tool  200  classifies the cell into any of the first to third categories based on the full charge capacity of the cell. The first to third categories are classified according to the size of the full charge capacity. The categories of the full charge capacities are in order of the first category, the second category, and the third category from the smallest. It is considered that the smaller the cell estimation capacity, the higher the deterioration degree. In this embodiment, the number of categories is three, but the number of categories can be appropriately changed. The number of categories may be 4 or higher and lower than 10, or may be 10 or higher. 
       FIG.  9    is a flowchart illustrating details of S 32 . With reference to  FIG.  9   , in S 41 , the service tool  200  determines whether the cell estimation capacity is smaller than a predetermined first threshold value (hereinafter, referred to as “Th 11 ”). Further, in S 42 , the service tool  200  determines whether the cell estimation capacity is smaller than a predetermined second threshold value (hereinafter, referred to as “Th 12 ”). Th 12  is higher than Th 11  (see  FIG.  10    described below). 
     When the cell estimation capacity is lower than Th 11  (YES in S 41 ), in S 421 , the cell is classified into the first category. When the cell estimation capacity is Th 11  or higher and lower than Th 12  (NO in S 41  and YES in S 42 ), in S 422 , the cell is classified into the second category. When the cell estimation capacity is Th 12  or higher (NO in both S 41  and S 42 ), in S 423 , the cell is classified into the third category. 
     A series of processes illustrated in  FIG.  9    is executed for each cell. When the processes illustrated in  FIG.  9    are executed for each cell of which a full charge capacity has been estimated in S 31  of  FIG.  8   , the process proceeds to S 33  of  FIG.  8   . A cell (that is, a cell of which a voltage has reached the discharging end voltage before the end of the discharging) classified into any of the first to third categories by the processes illustrated in  FIG.  9    is also referred to as a “diagnosis target cell” hereinbelow. 
     With reference to  FIG.  8    with  FIGS.  1  and  2    again, in S 33 , the service tool  200  determines whether all of the diagnosis target cells have been classified into the third category (S 423  of  FIG.  9   ). Further, in S 34 , the service tool  200  determines whether a cell that has been classified into the first category (S 421  of  FIG.  9   ) exists among the diagnosis target cells. 
     When all of the diagnosis target cells have been classified into the third category (YES in S 33 ), in S 341 , the service tool  200  determines that the drive battery  11  is new. When a cell that has been classified into the first category exists among the diagnosis target cells (NO in S 33  and YES in S 34 ), in S 343 , the service tool  200  determines that use of the drive battery  11  is not continuable (that is, the use of the drive battery  11  in the vehicle  100  cannot be continued). When all the diagnosis target cells are not classified into the third category and no cell that has been classified into the first category exists among the diagnosis target cells (NO in both S 33  and S 34 ), in S 342 , the service tool  200  determines that the use of the drive battery  11  is continuable (that is, the use of the drive battery  11  in the vehicle  100  can be continued). 
       FIG.  10    is a diagram for describing the determination (S 33 , S 34 , and S 341  to S 343  of  FIG.  8   ) of a battery life in the deterioration diagnosis method of the assembled battery according to the embodiment of the present disclosure. 
     With reference to  FIG.  10   , in the assembled battery A, all the diagnosis target cells have been classified into the third category. For this reason, a positive determination is made in S 33  of  FIG.  8   , and the assembled battery A is determined to be “new” (S 341 ). In each of the assembled batteries B and C, all the diagnosis target cells have not been classified into the third category, and no cell that has been classified into the first category exists among the diagnosis target cells. For this reason, negative determinations are made in both S 33  and S 34  of  FIG.  8   , and the use of each of the assembled batteries B and C is determined to be “continuable” (S 342 ). In an assembled battery D, a cell that has been classified into the first category exists among the diagnosis target cells. For this reason, a negative determination is made in S 33  of  FIG.  8    and a positive determination is made in S 34  of  FIG.  8   , and the use of the assembled battery D is determined to be “not continuable” (S 343 ). 
     With reference to  FIG.  8    together with  FIGS.  1  and  2    again, when any of the processes of S 341  to S 343  is executed, the process proceeds to S 35 . In S 35 , the service tool  200  transmits, to the vehicle  100 , diagnosis results (any of the state where the assembled battery is new/the state where the use of the assembled battery is continuable/the state where the use thereof is not continuable) of S 341  to S 343 . The diagnosis result received by the vehicle  100  is stored in, for example, the storage device  53  of the HVECU  50 . When the process of S 35  is executed, a series of processes illustrated in  FIG.  8    ends. 
       FIG.  11    is a flowchart illustrating processes executed by the vehicle  100  after the execution of the processes illustrated in  FIG.  8   . The process illustrated in this flowchart is started when, for example, the service tool  200  is removed from the vehicle  100  after the processes illustrated in  FIG.  8    ends. However, a condition of starting a process illustrated in  FIG.  11    is not limited thereto, and can be arbitrarily set. For example, the HVECU  50  may start the process illustrated in  FIG.  11    in response to a request from a user after the processes illustrated in  FIG.  8    ends. Each step illustrated in  FIG.  11    is executed by the HVECU  50 . 
     With reference to  FIG.  11    together with  FIGS.  1  and  2   , in S 51 , the HVECU  50  determines whether the use of the drive battery  11  in the vehicle  100  is continuable, using the deterioration degree of the drive battery  11 , which has been estimated by the service tool  200 . Specifically, when the state of the drive battery  11  corresponds to “the state where the drive battery  11  is new” or “the state where the use of the battery is continuable”, the HVECU  50  determines that the use of the drive battery  11  in the vehicle  100  is continuable (YES in S 51 ), and the process proceeds to S 52 . On the other hand, when the state of the drive battery  11  corresponds to the state where “the use is not continuable”, the HVECU  50  determines that the use of the drive battery  11  in the vehicle  100  is not continuable (NO in S 51 ), and the process proceeds to S 54 . 
     In S 52 , the HVECU  50  executes a start control of the engine  31 . Specifically, the HVECU  50  controls the MG  21   a,  the MG  21   b,  and the engine  31  such that the engine  31  is started. The HVECU  50  controls the MG  21   a  and the MG  21   b  via the PCU 24 . In the start control of the engine  31 , the MG  21   a  executes the cranking of the engine  31  using power supplied from the drive battery  11 . The cranked engine  31  starts combustion. As such, the engine  31  is started. 
     Subsequently in S 53 , the HVECU  50  charges the drive battery  11  with power generated by the engine power generation. As such, power generated by the MG  21   a  using drive power output from the started engine  31  is input to the drive battery  11  via the PCU  24  and the SMR  14 . When the SOC of the drive battery  11  becomes a predetermined value or higher, the HVECU  50  ends the charging. The HVECU  50  may return the SOC of the drive battery  11  to the SOC value before the diagnosis by the process of S 53 . Alternatively, the HVECU  50  may charge the drive battery  11  until the vehicle  100  turns to a state of being capable of EV traveling. When the process of S 53  (the charging of the drive battery  11 ) is ended, a series of processes illustrated in  FIG.  11    ends. 
     In S 54 , the HVECU  50  sends a notification indicating that the use of the drive battery  11  in the vehicle  100  is not continuable. The HVECU  50  may control the notification device  104  such that it prompts a replacement of the drive battery  11 . For example, the notification device  104  may display a message indicating that a time to replace the drive battery  11  has arrived. However, the present disclosure is not limited thereto, and the notification device  104  may prompt the replacement of the drive battery  11  by sound (including voice). Alternatively, the HVECU  50  may send a predetermined notification (for example, a notification indicating that a replacement of the drive battery  11  is required) to a terminal (for example, a smartphone or a wearable device) carried by the user of the vehicle  100 . When the process of S 54  is executed, the series of processes illustrated in  FIG.  11    ends. 
     After the process of S 54 , the drive battery  11  is replaced. In this embodiment, a battery pack including the drive battery  11  is replaced. However, the present disclosure is not limited thereto, and the assembled battery may be replaced (rebuilt) by a unit of a cell. The drive battery  11  removed from the vehicle  100  may be used for other purposes. 
     As described above, the deterioration diagnosis method of the assembled battery according to this embodiment includes the series of processes illustrated in  FIG.  3   , the series of processes illustrated in  FIG.  8   , and the series of processes illustrated in  FIG.  11   . 
     In the processes illustrated in  FIG.  3   , the service tool  200  discharges each cell while measuring the voltage of each cell included in the drive battery  11  (S 15  and S 16 ) in the vehicle  100  including the engine  31  (the internal combustion engine), the MG  21   a  (the motor that executes the start processing of the engine  31 ), and the drive battery  11  (the assembled battery) that supplies power to the MG  21   a.  The service tool  200  repeatedly determines, during the discharging of each cell, whether the drive battery  11  becomes unable to supply the power required for the start processing of the engine  31  to the MG  21   a  when the discharging is continued (S 19 ). Upon determining, during the discharging of each cell, that the drive battery  11  becomes unable to supply the power required for the start processing of the engine  31  to the MG  21   a  when the discharging is continued (NO in S 19 ), the service tool  200  ends the discharging (S 20 ). 
     After the end of the discharging, the service tool  200  estimates the deterioration degree of the drive battery  11  by the processes illustrated in  FIG.  8   , using the voltage data, which is acquired during the discharging, of at least one cell. Specifically, the service tool  200  determines whether the state of the drive battery  11  corresponds to any of the state where the drive battery  11  is new (the deterioration degree is low), the state where the use of the battery is continuable (the deterioration degree is approximately intermediate), or the state where the use thereof is not continuable (the deterioration degree is high) (S 341  to S 343 ). 
     With reference to  FIG.  11   , the vehicle  100  determines whether the use of the drive battery  11  in the vehicle  100  is continuable, using the deterioration degree of the drive battery  11 , which has been estimated by the service tool  200  (S 51 ). When the vehicle  100  determines that the use of the drive battery  11  in the vehicle  100  is continuable (YES in S 51 ), the MG  21   a  executes the start processing of the engine  31  (S 52 ). Then, the vehicle  100  charges the drive battery  11  with power generated by using drive power output from the started engine  31  (S 53 ). 
     With the deterioration diagnosis method of the assembled battery, it is possible to easily execute the start processing of the engine  31  (the internal combustion engine) after the discharging for the deterioration diagnosis of the drive battery  11  (the assembled battery) is executed. Further, it is also possible to easily charge the drive battery  11  that has been discharged for the deterioration diagnosis. In the above deterioration diagnosis method, the drive battery  11  is discharged while it is mounted on the vehicle  100 . Since the full charge capacity of the drive battery  11  to be diagnosed is 5 kWh or smaller, it is possible to execute the diagnosis with sufficient throughput. 
     The processes illustrated in  FIG.  3    may be appropriately changed. Further, the end condition of the discharging can also be appropriately changed. For example, the third end condition (S 18  of  FIG.  3   ) may be omitted if unnecessary. Alternatively, an additional end condition may be added to the first to third end conditions. 
     In the above embodiment, the discharging unit  211  and the estimation unit  212  in the service tool  200  are embodied by the processor  201  and a program executed by the processor  201 . However, the present disclosure is not limited thereto, and the discharging unit  211  and the estimation unit  212  may be embodied by dedicated hardware (an electronic circuit). 
     Further, functions of the discharging unit  211  and the estimation unit  212  may be implemented in the vehicle  100 .  FIG.  12    is a diagram illustrating a modified example of the HVECU  50  illustrated in  FIG.  2   . With reference to  FIG.  12   , an HVECU  50 A mounted on the vehicle  100  may include the discharging unit  211  and the estimation unit  212 . The discharging unit  211  and the estimation unit  212  in the HVECU  50 A may be embodied by the processor  51  and a program executed by the processor  51  (for example, a diagnosis program stored in a storage device  53 A). 
     In the above embodiment, the assembled battery mounted on the HEV which does not include an inlet for a plug-in is a target of the deterioration diagnosis. However, the present disclosure is not limited thereto, and an assembled battery mounted on a plug-in hybrid electric vehicle (PHEV) which includes an inlet for a plug-in may be a target of the deterioration diagnosis. 
     In some embodiments, not all of the cells are connected in series in the assembled battery of which the deterioration is diagnosed by any of the above-described methods (see  FIG.  2   ). The structure of the assembled battery of which the deterioration is diagnosed is arbitrary.  FIG.  13    is a diagram illustrating a modified example of the assembled battery illustrated in  FIG.  2   . For example, an assembled battery  500  illustrated in  FIG.  13    may be a target of the deterioration diagnosis. The assembled battery  500  includes N parallel cell blocks (that is, parallel cell blocks CB- 1  to CB-N). Each of the parallel cell blocks CB- 1  to CB-N includes a plurality of cells connected in parallel. The number of cells connected in parallel in each parallel cell block is arbitrary, but in the example illustrated in  FIG.  13   , it is three. The parallel cell blocks CB- 1  to CB-N are connected in series via a power line. 
     The embodiment disclosed herein needs to be considered as illustrative in all points and not restrictive. The scope of the present disclosure is shown not by the above description of the embodiments but by the claims, and is intended to include meanings equivalent to the claims and all modifications within the scope thereof.