A battery system including: a plurality of battery modules; a plurality of switches arranged in a circuit including the plurality of the battery modules, the plurality of the switches being configured to switch connection of the battery modules between a series state and a parallel state; a storage device that stores at least one abnormality pattern; and a control device configured to: i) control switching of each of the plurality of the switches; and ii) control switching of the switches other than the predetermined switch such that the battery modules rue not in a short-circuited state using the abnormality pattern when the predetermined switch is unable to be controlled.