Method of detecting and resolving memory effect

A method of detecting and resolving a memory effect capable of detecting the memory effect with ease and with high precision and resolving even when the vehicle is in motion is provided. A current in a secondary battery is detected, a variation DELTA SOC in a residual battery capacity for a predetermined time period is calculated according to at least current integration by multiplying the detected current by a predetermined charge efficiency (S302), a temperature of the secondary battery is detected and a variation DELTA V in a no-load voltage for the predetermined time period is calculated based on the detected current, and an internal resistance corresponding to the detected temperature and the SOC is calculated (S303). A ratio k of the variation in the no-load voltage to the variation in the residual battery capacity is calculated (S304). If the ratio exceeds a predetermined threshold value kst, then the battery is judged to have a memory effect (S307), and the usage range of the SOC is extended for a predetermined time period (S308) or the correction of the SOC using voltages is prohibited for a predetermined time period(S309).