A battery unit includes a module assembly, a housing that houses the module assembly, and a blower. The module assembly includes a stack of battery modules, and defines a first surface and a second surface opposite to the first surface. The blower is disposed at an end of the module assembly. A rotation shaft of the blower is located between a first plane that includes the first surface and a second plane that includes the second surface. The blower is configured to supply air toward the first surface of the module assembly in a direction perpendicular to a stacking direction of the battery modules. The air is supplied over a range that is substantially equal to a dimension of the module assembly in the stacking direction.