Firstly, and if your still with us, I'd look into close encounters of the 4th kind as Kedawa suggestes above. This can be a bugger with Amiga problems.
If all's well and your still here with us and in one piece I'd illiminate the battery, sounds like it could be on its way out. If your still losing time the next step is to check contacts.
I've personally not had this problem in my 1200 but have had it in a couple of A2000s which turned out to be duff batteries.
Good luck and keep us updated.
