BATTERY SYSTEM

A main object of the present disclosure is to provide a battery system capable of avoiding an over charge with a simple sensor element. The present disclosure achieves the object by providing a battery system comprising: a battery module including a battery pack A including a plurality of battery cells connected in series, and a battery pack B including a plurality of battery cells connected in series, connected in parallel, a monitoring unit configured to monitor a condition of the battery module, and a control unit configured to control at least a charge of the battery module, and the monitoring unit includes: a first current sensor configured to measure a total current Iof the battery pack A, and a second current sensor configured to measure a total current Iof the battery pack B, and the control unit includes: a calculating section configured to calculate a determining value based on the total current Iand the total current I, and a determining section configured to determine an occurrence of an over charge based on the determining value.