Patent ID: 8148946

Claim:
A battery pack comprising: first through third external terminals connected to positive and negative power supply terminals of a charge device and a voltage detection terminal, respectively, wherein the charge device stops charging when a voltage at the voltage detection terminal is lower than a predetermined voltage; a secondary battery connected between said first external terminal and said third external terminal; a protection circuit controlling ON/OFF of first and second switching elements provided on wiring between said secondary battery and a load or said charge device by detecting an overcharge, an overdischarge and an overcurrent of said secondary battery; a first thermistor connected between said second external terminal and said third external terminal; a series circuit provided in a vicinity of said secondary battery and containing a second thermistor and a resistor connected in parallel to said secondary battery; and a third switching element provided in said battery pack separately from said first and second switching elements and connected between said second external terminal and said third external terminal, wherein said protection circuit turns on said third switching element, independently from said first and second switching elements, and short-circuits between said second external terminal and said third external terminal when a detection is made by said second thermistor that a temperature of said secondary battery exceeds a predetermined temperature.