Hi Tony,
Most GPS modules do have a small button cell in them to power the almanac memory which is recharged by the circuitry, but they can eventually die. Unfortunately the 'workings' are normally sealed inside a metal screen and the cells are usually spot-welded in to a holder on the board, so not replaceable. If you are having serious issues, it might be worth trying a replacement GPS - available from the PilotAware store.
Regards
Peter