The battery, she just wouldn't hold a charge like she used to. So I went my usual route -- the big Internet behemoth named after a South American rain forest. Wow, was that ever confusing. No-name replacement batteries, varying voltages and watt-hour specs, reviews that were all over the place, including diverging opinions on which screwdrivers to use for my MacBook Pro... I went searching elsewhere (here) and I'm glad I did.
From finding what I needed, including the EXACT correct screwdriver, quickly and easily, the whole process was great. Got the new battery and screwdriver, opened the package (good packaging, too, no annoying air bags that I had to pop and throw away -- I was able to recycle the whole thing!) and opened my computer and had the whole thing replaced in less than 15 minutes. The battery lasts just like new and I couldn't be happier.
The bottom line -- when it comes to specific Apple replacement parts, I won't go anywhere else now. I may have paid $5 more than I would somewhere else, but I know the battery is going to work in my machine and the hassle factor is 0!
When you're taking the bottom of your computer off, just go slow, get a piece of paper and as you take each screw out, put it in a matching place on the paper. Makes it super easy to find the exact right screw to go back in its original hole. Makes it hard to go wrong (unless your repair session is interrupted by a herd of wild dogs, but then you have more serious problems...)