BATTERY SYSTEM AND A CONTROL METHOD THEREFOR

A battery system includes an electricity storage device (70) including a plurality of battery units (BU). The electronic control device (100) is configured to be capable of switching a travel mode of the vehicle between a CD mode and a CS mode. The electronic control device (100) is configured to calculate a vehicle state of charge at a higher value (SOC (A)) than an average state of charge (Smid) when the average state of charge (Smid) is higher than a threshold value (D), and calculate the vehicle state of charge at a lower value (SOC (B)) than the average state of charge (Smid) when the average state of charge (Smid) is equal to or lower than the threshold value (D). The threshold value (D) is set at a lower value than a center value (C) between an upper limit value (A) and a lower limit value (B) of the vehicle state of charge.