An object of the present disclosure is to provide a secondary battery system that functions at high voltage. The present disclosure attains the object by providing a secondary battery system comprising: a hybrid ion battery provided with a cathode active material layer having a cathode active material that contains a metal element capable of taking two kinds or more of a positive valence, an anode active material layer having an anode active material that contains a metal element capable of taking a valence of +2 or more, and an electrolyte layer containing an alkali metal ion and fluoride anion, and formed between the cathode active material layer and the anode active material layer; and a controlling portion that controls charging and discharging of the hybrid ion battery; wherein the controlling portion controls discharging so that a potential of the cathode active material includes a potential range higher than 0.23 V (vs. SHE).