The object of the present invention is to provide a battery system in which reductive decomposition of a Ge-containing solid electrolyte material is restricted. The present invention attains the object by providing a battery system including a battery and a control apparatus, wherein the battery has a cathode active material layer containing a cathode active material, an anode active material layer containing a Si-containing anode active material, and an electrolyte layer formed between the cathode active material layer and the anode active material layer, at least one of the anode active material layer and the electrolyte layer contains a Ge-containing solid electrolyte material, and the control apparatus is an apparatus to control an electric potential of the Si-containing anode active material so as to be reduction potential or less of the Ge-containing solid electrolyte material.