Patent ID: 7839116

Claim:
A power supply device incorporated in a system and receives a supply of electric power from the system and supplies electric power to a system electric power-consuming apparatus, said power supply device comprising: a first battery that is chargeable and dischargeable and has a first characteristic which is quick deterioration in a low state of charge having a low level of dischargeable electric power; a second battery that is chargeable and dischargeable and has a second characteristic which is quick deterioration in a high state of charge having a high level of dischargeable electric power; a voltage adjustment structure that adjusts a first voltage as a voltage of a first voltage system connected with the first battery and a second voltage of a second voltage system connected with the second battery; a first state of charge computation module that computes a first state of charge as a dischargeable electric power from the first battery based on the state of the first battery; a second state of charge computation module that computes a second state of charge as a dischargeable electric power from the second battery based on the state of the second battery; and a control module that, when the system is off, under condition that the computed first state of charge is less than a first predetermined state of charge which is lower than a state of charge at a full charge level and the computed second state of charge is more than a second predetermined state of charge which is chargeable of the first battery, controls said voltage adjustment structure to cause the state of charge of the first battery to become more than the first predetermined state of charge by transmission of electric power between the first battery and the second battery.