Battery apparatus

There is provided a battery apparatus (1) mounted in a vehicle that is not subjected to forced draft, the battery apparatus including a plurality of rectangular parallelepiped batteries (2) stacked in a direction vertical to a traveling direction of the vehicle; a rectangular parallelepiped battery box (3) that accommodates the plurality of rectangular parallelepiped batteries (2) therein; and a heat equalizing plate (10) that is brought into contact with the plurality of rectangular parallelepiped batteries (2).