A rechargeable hearing aid battery includes a stack of active materials forming a core, a two-part casing including an inner casing and an outer casing, and a grommet. The grommet includes an opening through which a conductive tab extends. The conductive tab is configured to electrically connect an electrode of the core to one of the outer casing and the inner casing. The grommet is configured to insulate a portion of the tab from the core and to insulate the core from one of the outer casing and the inner casing. Furthermore, the grommet is configured to separate the inner casing from the outer casing and to seal a gap formed between the inner and outer casing.