Patent ID: 8521458

Claim:
A device which detects a state of charge of an electric storage device, comprising: a comparator which, before comparing an electric storage device voltage, is supplied with a first predetermined voltage that has been set at a threshold value that is within a voltage change range when the electric storage device repeats charging and discharging, is supplied with a second predetermined voltage that has been set at a threshold value that is within a voltage change range when the electric storage device repeats charging and discharging, and then compares the electric storage device voltage to the first and the second predetermined voltages; a measuring unit which measures a first current value at a specific time when a voltage of the electric storage device becomes equal to the first predetermined voltage and a second current value at a time when the voltage of the electric storage device becomes equal to the second predetermined voltage; and a detecting unit which calculates an open end voltage of the electric storage device based on the first current value, the second current value, the first predetermined voltage, and the second predetermined voltage and calculates a state of charge corresponding to the calculated open end voltage based on a correspondence relationship between the open end voltage and the state of charge stored in advance.