My old battery was losing power very quickly and was "puffing out" from its cover so I thought it was time to get a new one.
Easy. I didn't even need to buy the $2.50 "coin" - just used my own US quarter :-)
This was my second repair using iFixit.com. My recommendation would be to get a new battery before your old one dies, or your computer gets discontinued. My husband has a G4 PowerBook and new batteries are no longer in stock so it seems that getting one sooner rather than later is a good idea.