A battery system includes a plurality of converters wherein each converter converts an electric power between a corresponding block of a plurality of blocks and an auxiliary battery. A first equalization control is a control for, when a vehicle is in a ReadyON state, operating a converter corresponding to a lower-voltage block, of at least one pair of blocks of the plurality of blocks having voltage variations exceeding a threshold value, such that the lower-voltage block is charged with an electric power supplied from the auxiliary battery. A second equalization control is a control for, when the vehicle is in a ReadyOFF state, operating a converter corresponding to a higher-voltage block, of at least one pair of blocks of the plurality of blocks having the voltage variations exceeding another threshold value, such that the auxiliary battery is charged with an electric power supplied from the higher-voltage block.