Method of detecting residual capacity of battery for use on electric vehicle

Abstract

Based on the difference between a battery voltage immediately after the battery is left to stand and the battery voltage upon elapse of the period of time after the battery has been left to stand, it is determined whether the battery has been in a charge mode or a discharge mode immediately before the battery is left to stand. If the battery has been in the charge mode, then a residual capacity is determined from the battery voltage at a predetermined time. When the battery is being discharged, then a maximum battery output is calculated based on a discharge current. If the residual capacity of the battery is determined as being virtually zero based on the maximum output, then the residual capacity is corrected with a corrective capacity for correcting for a change in the residual capacity due to a degradation of the battery, thus determining the residual capacity of the required charge quantity is calculated from the detected residual capacity and a stored rated capacity of the battery, and a temperature corrective coefficient for correcting the required charge quantity is determined. The residual capacity of the battery is determined based on an actual charge quantity indicative of an integrated average charging current at predetermined periods and the charging efficiency based on battery voltage during charging.