Various embodiments of the invention provide an enclosure for a metal-air
battery assembly for an extended wear hearing aid. The enclosure includes
a diffusion control element having a dimensional property configured for
controlling oxygen and moisture diffusion into the metal-air battery
assembly to maintain a minimum battery voltage when the hearing aid is
operating and worn in an ear canal of a user over an extended period. In
an embodiment, the enclosure can comprise a shell with a base end having
an opening therein forming a cavity within the shell and a base cap for
covering the opening of the base end. A diffusion element is disposed on
the base cap. In an embodiment, the diffusion element comprises a laser
drilled precision micro hole having an aspect ratio of least about four
and a diameter in the range of about 10 to 15 microns.