Interesting point - it could indeed be that it goes cold, the symptoms sounds like it. I didn't think of that. Stand-alone GPS units have a clock, and NVRAM to hold the last ephemeris data. Maybe the chipset in the N810 is so bare-bones that it doesn't have its own NVRAM? If so, then as you say, it should be reasonably easy to fix (unless the GPS chipset can't be fed ephemeris data from the N810.. that would be a major design flaw).