DETERMINATION SYSTEM, VEHICLE, AND DETERMINATION METHOD

A battery ECU is a system that determines a battery assembly that stores power used for running a vehicle and that is mounted on the vehicle in a replaceable state, the system comprising: a processor; a memory that stores a genuine product characteristic that is a temperature change characteristic of a genuine product, the temperature change characteristic being a characteristic of an index which changes with temperature of the battery assembly and when not being charged or discharged; and a sensor that acquires a determination target characteristic that is a temperature change characteristic of the index of the battery assembly after replacement mounted on the vehicle when not being charged or discharged. The processor compares the determination target characteristic acquired by the sensor with the genuine product characteristic stored in the memory, and determines whether the battery assembly mounted on the vehicle is the genuine product from a comparison result.