CELL SYSTEM

Exhaust of combustible gas is satisfied while reducing a rating air volume of fans. A battery system comprising a battery rack having a plurality of battery sub-racks in which a plurality of battery modules are accommodated, wherein the battery sub-racks each include a first fan and a gas detecting apparatus, the battery rack includes a second fan configured to exhaust the air exhausted from the first fan of a plurality of the battery sub-racks, the second fan is configured to have a rating air volume larger than the rating air volume of the first fan, and when a predetermined gas is sensed by the gas detecting apparatus of one of the battery sub-racks, the second fan is driven in a state in which the first fan of the one of the battery sub-racks is driven, and the first fans of the battery sub-racks other than the one of the battery sub-racks are stopped.