A power system (403) for an electric vehicle comprises a rechargeable battery (400), a battery control device (401) for controlling the state of the battery (400), including the remaining charge of the battery, and a charger (402) for charging the rechargeable battery (400). The charger (402) includes discharge means (404) for refreshing the rechargeable battery (400) and discharge control means (405) for controlling the refreshing by the discharge means (404) based on a refreshing signal from the battery control device (401).