Simple, fast battery replacement
When I opened my MacBook Pro (mid-2009), the cursor was moving around the screen and clicking randomly. It looked possessed. Clicked on battery status, held down the "option" button, and it said "Service Battery!" So that meant the battery was swelling inside, causing the trackpad to be depressed—just like me when I found this out. I was worried it was going to Galaxy 7 and burn my place down.
SO EASY. Five minutes. Fun to do. BUT the issue was ordering the Y1 Tri Wing Driver that those two pesky little battery screws inside require. *Very annoying* Amazon said it was delivered when it wasn't. I ordered another one, and this one did arrive 2 days later, $5 for each. That was my only hang up: finding that stupid screwdriver and actually getting it. The actual fix was very simple—open the back, take out the old battery, put the new one in, close the back. Voila!
Use iFixit first. Simple, easy information and clear video and repair guide. Great experience.
And thank you to Matt Fuss for clearly stating that they can't put these batteries on planes anymore, so I had to approve that it would be slower in getting to me from CA. It was clear, efficient, and iFixit refunded the extra $ I had paid for fast delivery to CT that was no longer possible. The best!