A battery system includes: an assembled battery having battery cells with a pair of electrodes, wherein one electrode of one cell is coupled with another electrode of another cell via a bus bar so that the cells are coupled in series with each other; a fluid supply element for supplying fluid to the bus bar and the electrodes so that the fluid conducts heat to and absorbs heat from the bus bar and the electrodes; and a partition for partitioning the bus bars and for providing multiple passages. The bus bar and the electrodes protrude from the cell. The passages are disposed outside of the assembled battery. The fluid is branched into the passages.