BATTERY SYSTEM

A main object of the present disclosure is to provide a battery system capable of avoiding an over discharge with a simple sensor element. The present disclosure achieves the object by providing a battery system comprising: a battery pack including a plurality of battery cells connected in series, a monitoring unit configured to monitor a condition of the battery pack, and a control unit configured to control at least a discharge of the battery pack, and the monitoring unit includes: a voltage sensor configured to measure a total voltage of the battery pack, a current sensor configured to measure a total current of the battery pack, and a temperature sensor configured to measure a temperature of the battery pack, the control unit includes: a calculating section configured to calculate capacity condition A of the battery pack at a first discharge cutoff voltage based on the total voltage and the total current, an estimating section configured to estimate capacity condition B of the battery pack at the first discharge cutoff voltage based on the total current and the temperature, a determining section configured to determine an occurrence of an over discharge based on the capacity condition A and the capacity condition B, and a voltage changing section configured to change the first discharge cutoff voltage to a second discharge cutoff voltage that is higher than the first discharge cutoff voltage, when the occurrence of the over discharge is determined.