To improve cycle life, by attaching a temperature sensor on the surface of a battery, controlling the discharge finishing voltage suitable to the detecting temperature, and the charge control voltage by a relational expression set beforehand, and providing an adequate charge and discharge condition in the using time.

At the charging side, a voltage detector 5 is provided in parallel to plural batteries 6 to which a temperature sensor 7 is provided on the case surface concurrently, and it is connected to a charger 3 through an ammeter 2 and a switch 1. By the data output from an operator 10 to which the data from the battery temperature detector 8 connected to the sensor 7 is input, the charge control voltage of the charger 3 is decided by a charge voltage controller 9. On the other hand, at the discharge side, the batteries 6 are connected to a switch 1 and a load 4 through the ammeter 2. The data output from the operator 10 is input also to a discharge finishing voltage controller 11, and the discharge finishing voltage of the load 4 is set by the controller 11. To the operator 10, the relational expression of the temperature and two voltages is set beforehand and registered, and the voltages are controlled by this relational expression.