To reactivate a battery reduced in capacity due to supercooling in a short time and to keep the normal operation of an external device using a battery as a power supply in a simple device by heating with a small alternating current generated by the battery.

A capacity CL is charged with a voltage UB of a battery formed by cells E1, E2,... En to operate a control circuit CC. A signal of detecting the temperature of the battery B by a temperature sensor TS is input to a comparator of CC through an input InCOMP1, and when supercooling is judged, the optimum frequency fP as a function of an internal temperature of the battery B is adjusted, the according to a pulse fP, a switch S1 is opened and closed to supply a pulse current IB to the battery B. IB is converted to energy by an internal resistor R1 to raise the temperature of an electrolytic solution. Thus, the battery reduced in capacity due to supercooling can be reactivated effectively in a simple device in a short time.