A secondary battery system that is light in weight and low in cost is provided, which comprises a plurality of secondary batteries connected in series. A plurality of first diodes each has an anode connected to a negative electrode of the corresponding secondary battery. A plurality of second diodes each has a cathode connected to a positive electrode of the corresponding secondary battery. A plurality of capacitors is each connected to a junction portion between the cathode of the first diode and the anode of the second diode. An alternating current power source is commonly connected to the junction portions through the capacitors.