A battery unit includes a battery and an insulation film, the battery includes a battery housing, a battery core disposed inside the battery housing, and a battery cover plate disposed on an end portion of the battery housing; the insulation film is coated on at least one side face of the battery housing, the insulation films on two adjacent battery units are bonded to each other in the preset direction to connect the plurality of battery units together; and the insulation film includes an extension portion, where the extension portion is formed by a top portion of the insulation film which protrudes from the battery cover plate and extends upward, the top plate is disposed on an upper side of the battery unit, a groove is provided on a lower side of the top panel, and at least part of the extension portion is accommodated in the groove.