To realize a power storage system in which the lifetime of a battery can be prevented from shortening by preventing repetition of low capacity charge/discharge as compared with the total battery capacity in a short time.

The power storage system comprises a power storage means consisting of two battery groups A-3 and B-4 having an equal chargeable/ dischargeable battery capacity, and a rectification system 2 for switching the power storage system between charging operation and discharging operation depending on the magnitude of power receiving from an energy supply/load unit 1. The rectification system 2 regards any one of two battery groups A-3 and B-4 as an object to be charged and the other as an object to be discharged based on the quantity of power being stored in each battery group.