A nonaqueous-electrolyte secondary battery charging/discharging method that provides a prolonged cyclic life. In the charging/discharging method, a secondary battery is continuously charged unconditionally until a charging capacity exceeds 20% of a full charging capacity. The charging is completed when the charging capacity exceeds 70% of a full charging capacity. A maintenance charging/discharging operation is performed to avoid the full charging capacity being in an error state when dV/dt exceeds a specified value “a” before a charging current exceeds 70% of the full charging capacity. Likewise, the maintenance charging/discharging operation is performed to avoid the full charging capacity being in an error state when dT/dt exceeds a specified value “b” before a charging current exceeds 70% of the charging capacity.