Abstract: A secondary battery system of connecting secondary batteries includes first output-unit switches, second output-unit switches, series-connection switches, a positive-side discharging output unit connected to second terminals of the first output-unit switches, a negative-side discharging output unit connected to second terminals of the second output-unit switches, a positive-side charging input unit connected between a positive terminal of one of the secondary batteries at one end of the secondary batteries and a first terminal of one of the first output-unit switches associated with the one of the secondary batteries at the one end of the secondary batteries, a negative-side charging input unit connected between a negative terminal of one of the secondary batteries at the other end of the secondary batteries and a first terminal of one of the second output-unit switches associated with the one of the secondary batteries at the other end of the secondary batteries, and a control unit.