BATTERY ASSEMBLY

According to the invention, an battery system with an arm formed by electrically connected a plurality of battery cells to each other is provided. The battery system includes: a temperature detection unit that is provided to each of battery cells; a cooling unit that cools the arm; and a control unit that identifies a maximum value from the temperatures of the battery cells measured by the temperature detection unit and controls the cooling unit so that the maximum value falls within a predetermined allowable temperature range.