The present invention addresses the issue of providing a battery system wherein reductive decomposition of a Ge-containing solid electrolyte material is suppressed. The present invention solves the issue by providing a battery system that is provided with a battery and a control apparatus. The battery system is characterized in that: the battery has a positive-electrode active material layer containing a positive-electrode active material, a negative-electrode active material layer containing a Si-containing negative-electrode active material, and an electrolyte layer formed between the positive-electrode active material layer and the negative-electrode active material layer; the negative-electrode active material layer and/or the electrolyte layer contains a Ge-containing solid electrolyte material; and the control apparatus controls potential of the Si-containing negative electrode active material to be equal to or lower than the reductive potential of the Ge-containing solid electrolyte material.