Charging rate monitoring apparatus for in-vehicle power supply, and in-vehicle power supply system

A charging rate monitoring apparatus for in-vehicle power supply configured to monitor charging rates of both a first power storage device and a second power storage device that supply power to a load via a power line, the apparatus comprising:

• a first switch connected between the power line and the first power storage device;
• a second switch connected between the power line and the second power storage device;
• a first monitoring circuit configured to output on/off signals to the first switch;
• and
• a second monitoring circuit configured to output on/off signals to the second switch,
• wherein the first monitoring circuit is configured to execute:
• a first process in which a terminal voltage of the first power storage device when the first switch is off is detected as a first open-circuit voltage, and a first charging rate is obtained based on the detected first open-circuit voltage and a relationship between the first open-circuit voltage and the first charging rate of the first power storage device, and
• a second process in which a first current flowing through the first power storage device is detected when the first switch is on, and the first charging rate is updated based on the first current,
• wherein the second monitoring circuit is configured to execute:
• a third process in which a terminal voltage of the second power storage device when the second switch is off is detected as a second open-circuit voltage, and a second charging rate is obtained based on the detected second open-circuit voltage and a relationship between the second open-circuit voltage and the second charging rate of the second power storage device, and
• a fourth process in which a second current flowing through the second power storage device is detected when the second switch is on, and the second charging rate is updated based on the second current.