Auxiliary battery status determination device and auxiliary battery status determination method

An auxiliary battery status determination method comprising:

• a detection step of detecting a magnitude of a terminal voltage of an auxiliary battery provided separately from a driving battery and a magnitude of a current flowing through the auxiliary battery, the driving battery being an electrical power source for a driving motor of a vehicle, and the auxiliary battery being an electrical power source for auxiliary equipment and having an output voltage lower than an output voltage of the driving battery;
• and
• an internal resistance calculating step of calculating an internal resistance of the auxiliary battery based on the magnitude of the terminal voltage and the magnitude of the current detected in the detection step,
• wherein in the internal resistance calculating step, the internal resistance is calculated based on the magnitude of the terminal voltage and the magnitude of the current detected in the detection step in a stable period that is before the auxiliary equipment is started and in which the magnitude of the terminal voltage and the magnitude of the current fall within predetermined fluctuation ranges, and the magnitude of the terminal voltage and the magnitude of the current detected in the detection step in a predetermined period after starting of the auxiliary equipment is detected.