All it has to be is IPX7 and take common lithium cells. GPSs, digicams, flashlights, even SPOT meet these criteria today.

The problem with the permanent battery is it's wearing down from the day it's made, meaning that as time goes on the owner becomes "less safe" since broadcast time goes down commensurately. Prudently running a self-test mode, of course, speeds this process. Methinks better to begin each hiking season with a fresh set of batteries. I suspect the expen$ive factory battery swaps are just a part of the current business model, but somebody will eventually break the mold and the rest will have to follow. They're just consumer electronic widgets, after all.

Cheers,