Well I've been taking a look around and see that there are a few "choices" even amongst the CR2025's, such as wired, barrel-shaped and the coin-shaped ones. I've a feeling I might need to actually look inside.
Also, I chanced to find the little hand manual that came with the PC originally (it was right in front of me on the bookshelves!) it is of absolutely no help battery-wise, but it surprised me a bit, to find that it speaks of DIMM rather than RAM... well, I did say it was old.
Can't quite decide what to do now, because I'm wondering about the condition of the main battery too, as it has been sitting idle for years. I think I should probably look at that first, just in case it has leaked, or anything (no outward signs, but...)
I don't suppose it would be safe to remove the battery and just run it on mains power? With our Fujitsu, you can, (and I do. I've never ever used it's battery pack.) But then again, I don't believe it's possible with the Rock, which we've always used with the battery in-situ... unless anyone knows differently, of course? Decisions, decisions