PURPOSE: To keep always the balance in capacity between a battery and charge- discharge electricity detecting element and precisely, quickly recharge the battery, the battery charging by providing a discharge circuit for compensating the quantity of the self discharge of the battery.

CONSTITUTION: A group of battery elements 1 and a load 6 are connected to a charge-discharge electricity detecting element 2 in series. When a switch 7 is turned on, a current charged in the group of battery elements 1 flows to the load 6 through the detecting element 2. When the switch 7 is turned off, a heat sensitive resistance element 9, current controlling resistance element 10, and the detecting element 2 are connected in series to form a closed circuit, an electric source of which is a battery element 8 only for the discharge of the detecting element 2. An element the resistivity of which reduces with increase of the temperature to increase the current corresponding to the thermal characteristics of the self discharge of the group of battery elements 1 such as thermistor element is used as the heat sensitive resistance element 9, thereby the change of the self discharge characteristics is compensated.