Closure element for battery casing

Locking element for sealing an opening of a battery housing, comprises a lid (5) exhibiting a connecting groove (6), into which a wall of the battery housing is insertable. A nondestructive and deformable connecting piece exhibiting a nipple (8), protrudes from the lid (7). An independent claim is also included for a housing comprising a first opening, in which a lid of the above locking element is accommodated, and a second opening, in which the nipple is accommodated.