CONTROL DEVICE

The control device includes a control unit that controls power supply from a main battery of the vehicle to a sub battery, and a calculation unit that calculates an estimated value of a full charge capacity of the main battery. When the error between the full charge capacity and the estimated value is larger than the predetermined value, the control unit calculates a power supply duration in which the power supply of the sub-battery to the load continues while the power supply is stopped, and a required time for eliminating the polarization of the main battery, and stops the power supply when the power supply duration is equal to or longer than the required time. The calculation unit calculates a voltage after a required time has elapsed since the power supply is stopped. After the voltage is calculated, the control unit resumes the power supply.