Welcome...your description sounds like a fairly typical battery leak to me. The battery hadn't been stressed (used) so it hadn't leaked. When you booted the machine and ran it the battery tried to charge and began to leak on the motherboard. It's always best to just go ahead and yank the battery when you take a machine like that out of storage (or before putting it in storage is even better).
Hope things get working for you....I've been rather lucky. I've gotten a 3000 and 4000 from EBay with no battery issues.
Bob
