I have a SPOT-2 and have not had any trouble with it at all. No problems with reliability whatsoever. If I'm going on a long trip, naturally I replace the batteries. SPOT is very explicit about the kinds of batteries that should go in the unit - so just use what's recommended. I think it's the lithium batteries, but my memory is sketchy on that. The important thing is to carefully read their manual and DO what they say.

cheers,
Pete #2