A battery system comprising: a plurality of battery modules (11, 12); a plurality of switches (R1, R2, R3) arranged in a circuit including the plurality of the battery modules (11, 12), the plurality of the switches (R1, R2, R3) being configured to switch connection of the plurality of the battery modules (11, 12) between a series state and a parallel state; and a control device configured to control switching of each of the plurality of the switches (R1, R2, R3), wherein: the series state is a state in which the plurality of the battery modules (11, 12) is connected in series, the parallel state is a state in which the plurality of the battery modules (11, 12) is connected in parallel, and the short-circuited state is a state in which terminals of at least one of the plurality of the battery modules (11, 12) is short-circuited; the battery system being characterized in that it also comprises a storage device that stores at least one abnormality pattern, the abnormality pattern being a switching plan of each of switches of the plurality of switches (R1, R2, R3) other than a predetermined switch which becomes unable to be controlled, the switching plan representing which of an open state and a closed state each of the switches other than the predetermined switch is switched to, and in that the control device is configured to control switching of the switches other than the predetermined switch such that the plurality of the battery modules (11, 12) is usable and not in a short-circuited state, using the abnormality pattern when the predetermined switch is unable to be controlled. a plurality of battery modules (11, 12); a plurality of switches (R1, R2, R3) arranged in a circuit including the plurality of the battery modules (11, 12), the plurality of the switches (R1, R2, R3) being configured to switch connection of the plurality of the battery modules (11, 12) between a series state and a parallel state; and a control device configured to control switching of each of the plurality of the switches (R1, R2, R3), wherein: the series state is a state in which the plurality of the battery modules (11, 12) is connected in series, the parallel state is a state in which the plurality of the battery modules (11, 12) is connected in parallel, and the short-circuited state is a state in which terminals of at least one of the plurality of the battery modules (11, 12) is short-circuited; the battery system being characterized in that it also comprises a storage device that stores at least one abnormality pattern, the abnormality pattern being a switching plan of each of switches of the plurality of switches (R1, R2, R3) other than a predetermined switch which becomes unable to be controlled, the switching plan representing which of an open state and a closed state each of the switches other than the predetermined switch is switched to, and in that the control device is configured to control switching of the switches other than the predetermined switch such that the plurality of the battery modules (11, 12) is usable and not in a short-circuited state, using the abnormality pattern when the predetermined switch is unable to be controlled. the series state is a state in which the plurality of the battery modules (11, 12) is connected in series, the parallel state is a state in which the plurality of the battery modules (11, 12) is connected in parallel, and the short-circuited state is a state in which terminals of at least one of the plurality of the battery modules (11, 12) is short-circuited;