OK, the A1200 itself doesn't have a battery, but, as yours has a cooling fan, i'm assuming yours has a turbocard inside it.
The first thing to do is turn the A1200 off, then flip it upside down, and remove the little trapdoor in the base. Inside should be a circuit board. If there isn't one, you haven't got a turbo card, so you shouldn't have a battery or a fan :-D
Take the board out by grabbing it, and pulling it away from the motherboard.
Now look for a battery. The ones on A1200 turbocards are usually coin-style ones, and are quite easily replaced.
