Patent ID: 7804277

Claim:
An apparatus for estimating a state of charge of a secondary battery, comprising: a storage unit that stores correlation information showing correlation between an open circuit voltage and a state of charge; a total-amount-of-electric-discharge detection unit that detects a total amount of electric discharge of the secondary battery; a correction unit that makes a correction to the correlation information in accordance with a relationship between the total amount of electric discharge and a predetermined threshold value; and an estimation unit that estimates a state of charge of the secondary battery by use of the corrected correlation information, wherein the storage unit stores, as the correlation information, correlation information achieved in an initial state where no memory effect is produced and correlation information achieved in a saturated state where the memory effect is saturated; and the correction unit makes a correction, when the total amount of electric discharge is equal to or greater than the predetermined threshold value, so as to replace the correlation information achieved in the initial state with the correlation information achieved in the saturated state, as well as making a correction, when the total amount of electric discharge is smaller than the predetermined threshold value, so as to acquire correlation information formed by mixing at a predetermined ratio the correlation information achieved in the initial state with the correlation information achieved in the saturated state.