The battery cellar includes a storage cabinet that stores a plurality of batteries, a power converter (an AC/DC converter and a DC/DC converter) electrically connected between the plurality of batteries stored in the storage cabinet and a power system to perform a bidirectional power conversion operation, and a server that controls the power converter to charge or discharge the plurality of batteries in response to a DR request from the power system. The server, based on a level of demand determined in accordance with a rank related to a degradation degree of a battery, suppresses the charging/discharging of a battery with a higher demand rank among the plurality of batteries as compared with the charging/discharging of a battery with a lower demand rank among the plurality of batteries.