An assembled battery system includes an assembled battery including a plurality of electric cell blocks connected in series, the electric cell blocks each including at least one nonaqueous electrolyte secondary battery provided with a negative electrode current collector formed of aluminum or an aluminum alloy, a voltage measuring unit configured to measure a plurality of voltages of the electric cell blocks, a controller which controls charge/discharge of the assembled battery in accordance with the measured voltages, and bypass circuits connected in parallel to the electric cell blocks, the bypass circuits each bypassing a current that flows from a negative electrode of one of the electric cell blocks to a positive electrode of the one of electric cell blocks when the measured voltage of the one of electric cell blocks is a negative value not greater than a threshold value.