The invention provides a protective device for batteries having a high energy density such as lithium ion batteries. The protective device includes a current conduction cutoff means having a current-conducting circuit comprising a voltage-detecting means for detecting the voltage of at least one battery being charged, a heat-generating resistance for starting the conduction of a current when the detected voltage exceeds a preset voltage, and a temperature fuse thermally coupled to the heat-generating resistance. When a state where battery voltage is higher than a preset value continues, a charging circuit for the battery is cut off by the temperature fuse and current output from the battery is disabled. The protective device further includes a battery-discharging means actuated upon detection of the fusing-down of the temperature fuse, so that the battery is disabled, and then placed in a dischargeable state.