The car power source apparatus is provided with a plurality of batteries, a temperature detection circuit, and an abnormal temperature rise prevention circuit. The temperature detection circuit detects electrical resistance change of a plurality of temperature sensors via a
voltage conversion circuit, converts
voltage conversion circuit output
voltage into a
digital signal via an A / D converter, and inputs that
signal into a
control circuit as a temperature
signal. The abnormal temperature rise prevention circuit is provided with comparators to compare output voltage from the voltage conversion circuit of the temperature detection circuit with a reference voltage and output an abnormal temperature
signal if battery temperature rises to a specified temperature, and a forced current
cut-off circuit connected to the comparators to detect a
comparator abnormal temperature signal and
cut-off battery current. The
control circuit and the abnormal temperature rise prevention circuit monitor battery temperature, and
cut-off battery current.