Abstract: An overcharge preventing device for a high energy density battery such as a lithium ion battery comprises a voltage sensor means for sensing a voltage of a battery that is being charged, a current feeder means for feeding a current to a heat generating means when a voltage sensed by said voltage sensor means exceeds a preset voltage, and a repeatedly usable thermal actuator means that is thermally coupled to said heat generation means incorporated in a charging current circuit. Upon overcharging of the battery, the thermal actuator means is actuated by heat generated from the heat generating means to interrupt feeding of a charging current to the battery. Upon elimination of an overcharged state, the charging current circuit in the thermal actuator means is resumed to recharge the battery.