I got my A500 out of storage. I was pleasantly surprised that there wasn't any damage to the side of the board I could see. Switch it on, caps lock light went on/off, power light flickered, then nothing.
I switched off the expansion, it booted (well, didn't check for the kickstart screen, but it sounded happy).
I pulled out the expansion, turned it over to see some battery fluffyness, but the main thing IMO is that the circuit pathways to (particularly) one chip have changed colour, so I assume that won't work any more. I'll take a picture once my wife finds the camera.