BATTERY SYSTEM

A battery system includes an assembled battery having a plurality of batteries connected in series, a discharge circuit having a first resistor and a discharge switch connected in series, which is connected in parallel to the respective batteries to discharge the respective batteries, a comparator that compares voltages of the respective batteries with a given voltage through the first resistor, and a diagnostic circuit that conducts a fault diagnosis of the discharge switch on the basis of comparison results of the comparator.