David Wilson wrote:
Cut the leads near the battery leaving them attached to the motherboard. Solder the new battery to the old leads - this avoids any damage to the motherboard.
To this thought I might add that if you can find a Mac battery holder, you could instead solder it to the board. Battery removal is the same, cut the leads close ot the battery, then desolder the wires down to the main board. Then solder the battery holder onto the main board in the holes left by the original battery leads. Soldering a battery holder to the main board is not a great adventure and is a minimal risk unless you get really carried away. (I'd be more worried about soldering a battery directly, they are more suseptable to heat damage than the main board.)
Thankx, Ed