DETERIORATION DIAGNOSIS APPARATUS OF ASSEMBLED BATTERY AND DETERIORATION DIAGNOSIS METHOD OF ASSEMBLED BATTERY

A deterioration diagnosis apparatus of an assembled battery includes at least one processor. The processor executes discharging of each of a plurality of cells included in an assembled battery mounted on a vehicle while measuring a voltage of each of the cells, and estimates 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 supplies power to the motor. The processor determines, during the discharging, whether the assembled battery becomes unable to supply power required for the start processing to the motor when the discharging is continued, and ends the discharging before the assembled battery becomes unable to supply the power to the motor.