I recently bought a "broken" macbook off ebay, took it apart, and got it running again, except the battery would not charge, and out of frustration took it to the genius bar (local) where the genius told me "you've got a bad battery - can't help with that, but I can replace this broken keyboard palmrest assembly for you" and they did. good to know all I needed was a battery, and good to get the deck replaced!
So, they are still replacing the palmrests that show breaks especially where the upper screen bumpers contact the deck. So I bought a used battery from ebay....
Funny thing is, I had the opportunity to go to Boston for a meeting a month later, and had some time, took my macbook (including the old non-working battery) to the genius bar in the Boston Apple Store, and the genius replaced my battery for free! He said that some batteries were not achieving their expected lifetime, and mine was one! So, it never hurts to ask (and if you get an answer you don't like ASKK AGAIN somewhere else!)
-raynman