Patent ID: 7733063

Claim:
An apparatus for calculating a quantity indicating a charged state of a battery being mounted on a vehicle, the battery powering a starter starting up an engine mounted on the vehicle, the apparatus comprising: a data acquiring unit configured to acquire a plurality of pairs of data consisting of current and voltage of the battery at predetermined sampling intervals during a cranking period of the engine in response to starting up the starter; a first calculating unit configured to calculate, as the quantity indicating the charged state of the battery, at intervals, a value of an internal resistance of the battery based on the plurality of pairs of data of current and voltage; a second calculating unit configured to calculate, based on the plurality of pairs of data of current and voltage, an open voltage difference which is a difference between a pseudo circuit-open voltage of the battery given before starting up the starter and a pseudo circuit-open voltage of the battery given after the cranking period; and a correcting unit configured to correct the value of the internal resistance based on the open voltage difference, the corrected value of the internal resistance being indicative of the charged state of the battery that supplies the current to the starter which is used in a starting-up operation for the engine.