The battery system is a combined system of a first battery and a second battery. The discharging curve (discharging characteristic) (311) of the first battery has a stable region (B1). The discharging curve (discharging characteristic) (321) of the second battery has a stable region (B2) in the range of voltage lower than the voltage in the stable region (B1) of the first battery and also has an unstable region (A2) in the range of voltage overlapping the voltage in the stable region (B1) of the first battery. The first battery and the second battery are connected in parallel so that, in a discharging process, the discharging state of the entire battery shifts from the stable region (B1) of the first battery to the stable region (B2) of the second battery.
