OK: here's one: I fly a J-3 Cub with no electrical system. The i520 internal battery is good for about two hours max. I have rigged up two small sealed lead-acid batteries in parallel that are rated at 12 @ 1.3Ah each (2.6 total) which should be good for another 4 hours or so. If I turn on the unit and THEN plug the battery power cord in, all seems well. If I plug the power cord in and THEN turn on the unit, it works fine for a while but after about 2-3 hours, goes to the GPS battery which is indicating half charged, then the unit will shut down. Testing the voltage on the batteries after, one may be 9-11 volts, one may be at a NEGATIVE 1-3 volts. Excuse me?
Makes no electrical sense. I don't think the unit is any hotter than it usually is being Sunlit in the cockpit.
I got one of the new Adventure Pilot external batteries and was excited that it was so small and would power an 520 for "a long time". The first time I plugged it in, I don't remember if I turned on the GPS first before plugging in the power cord. The battery powered the unit for the first hour without apparent problems. Next flight plugged it and and nothing; it did not work after that: dead. Thinking it had drained itself, plugged it in. Blue charge light on the charger, no red charge light on the battery. The 12.1V light would flash (meaning a defective battery, according to the manual) and that's it. Did I funk out the new battery by plugging it into the unit? That would make no sense. A new battery is on the way (I think) and I'd rather not mess it up.
Thoughts? My electrical brain has no answers to this one and everyone else just says Huh. Really.