A diagnostic technique for determining whether the degradation of a rechargeable battery is normal or abnormal is provided.A device for determining whether the degradation of a rechargeable battery is normal or abnormal comprises a device for measuring a degradation indicator of a rechargeable battery 18, a device for determining the usage quantity of the rechargeable battery, and a device for comparing the usage quantity with a reference usage quantity in the case where the measured degradation indicator exceeds a reference degradation value.