Patent ID: 7375498

Claim:
A battery pack comprising rechargeable batteries, a temperature sensor thermally joined to the rechargeable batteries to detect battery temperature via change in electrical resistance, a series resistor connected in series with the temperature sensor, and a protection circuit driven by the rechargeable batteries to detect battery temperature from change in the electrical resistance of the temperature sensor; wherein the protection circuit is provided with a temperature measurement switch which is connected in series with the series connection of the temperature sensor and series resistor and which supplies battery power to the temperature sensor and series resistor in the ON state and does not supply battery power to the temperature sensor and series resistor in the OFF state to reduce power consumption of the rechargeable battery, a sample-and-hold circuit which detects and retains the voltage at a measurement node which changes voltage as temperature sensor electrical resistance changes, and a timing circuit which controls timing for sampling and retention of the detected voltage by the sample-and-hold circuit and timing for turning the temperature measurement switch ON, wherein the timing circuit switches the temperature measurement switch ON and OFF with a fixed period, the sample-and-hold circuit samples and retains detected voltage when the temperature measurement switch is ON, and battery temperature is determined via the detected voltage which is sampled and retained.