A battery system includes a battery module having a plurality of assembled batteries. Battery monitoring circuits are provided to correspond to each of the assembled batteries of the battery module. A control circuit controls operation of the battery monitoring circuits. A first signal transmission path transmits signals that are input and output between the battery monitoring circuits and the control circuit. A first isolation element is connected to the control circuit, and a second isolation element is connected to the battery monitoring circuit. The first signal transmission path is isolated from the control circuit by the first isolation element and is isolated from the battery monitoring circuit by the second isolation element. The electrical potential of the first signal transmission path is a floating potential in relation to the electrical potentials of the control circuit and battery monitoring circuits.