Battery system

A battery system(1), which allows adjustment of balance of the voltages among the chargeable batteries while preventing electric loss, includes a plurality of battery modules(21)(22)(23)(24)(25) connected in series, each battery module including a plurality of battery cells(31) in a manner chargeable and dischargeable through positive and negative electrode terminals(32)(33). The battery system includes a charging/discharging control unit(14) connected between both electrodes of the plurality of battery modules connected in series to simultaneously charge the plurality of battery modules. The battery system also includes a voltage detector(15) for detecting a voltage of each of the battery modules. Charge discharged from the battery module whose voltage is higher than the voltages of the other battery modules is boosted to a predetermined voltage to be simultaneously supplied to the plurality of battery modules.