A post-deterioration performance estimating apparatus wherein a post-deterioration performance value indicates performance of an energy storage device. The apparatus includes a post-deterioration performance estimator is configured to electronically estimate the post-deterioration performance value at a deterioration point using (1) a relation between a cumulative operating period and a resistance value, (2) a relation between the resistance value and energy storage capacity, and (3) the cumulative operating period at the deterioration point. Alternatively, the post-deterioration performance estimator is configured to electronically estimate the post-deterioration performance value at a deterioration point using (1) a relation between an equilibrial capacity decreased amount, (2) a kinetic capacity decreased amount, and (3) a cumulative operating period at the deterioration point.