Vehicle-mounted power supply system and method for detecting state of battery contained therein

An on-vehicle power supply system, comprising:

• a main battery,
• a sub battery connected in parallel with the main battery,
• a voltage adjuster which controls a voltage of power supplied from the main battery and the sub battery, and
• a state detector which detects a state of the sub battery,
• wherein:
• the state detector comprises:
• a first calculating unit which obtains a first internal resistance that contains a reaction resistance and a parts resistance of the sub battery,
• a second calculating unit which obtains a second internal resistance that contains a reaction resistance of the sub battery, and
• a state determining unit which determines a state of the sub battery,
• the first calculating unit calculates the first internal resistance based on a voltage drop amount and an inrush current of the sub battery when supplying power to a load,
• the second calculating unit calculates the second internal resistance based on a relation between a voltage and a current of the sub battery when forcedly discharging the sub battery by controlling the voltage adjuster immediately after calculating the first internal resistance and thereafter once or more, and
• the state determining unit determines the state of the sub battery based on the first internal resistance and a transition of the second internal resistance.