Battery capacity calculating method

The present invention is relative to a battery capacity calculating method including a reference discharge curve calculating step of finding a discharge curve, operating as a reference, a corrected voltage calculating step of correcting a measured voltage V1 of the battery with a component of an electrical resistance to find a corrected voltage V, and a capacity calculating step of finding the discharging capacity of the battery from the discharge curve, operating as a reference, using the corrected voltage V. The capacity calculating step includes a sub-step of calculating a capacity deterioration index S, as a ratio of capacity decrease caused by battery deterioration. The discharging capacity, calculated from the discharging capacity, operating as a reference, using the corrected voltage V, is further multiplied with the capacity deterioration index S to calculate the discharging capacity.