My Late 2009 Macbook's (the original white unibody) battery died suddenly last summer. I checked with the local Apple retailer but they charged me almost twice the price of a new battery and they also wanted me to leave the laptop for two or three days at their shop. So I checked for a replacement and I remembered that some years ago I had a new iPod battery from iFixit.
Sadly, back then they had no new batteries for my model, so I had to wait and live off the wall charger for a while. That was frustrating because this is my main computer and I work on the go almost everyday, and not every place has a wall charger.
So when I saw iFixit had batteries for sale again I jumped in.
It was fairly easy to replace the battery, I just needed the screwdrivers (I had the Torx and ordered the rare Tri-wing) and a bit of patience. My greatest problem was the upper-left side plastic around one screw of the DVD drive, which didn't let the battery gently slip in. But I removed that screw, ditched the plastic piece and the battery wen it like a charm.
Anyway, I hope Apple go back to easy replaceable batteries. They weren't much larger and they were more practical.
Have your screwdrivers in place, take care with the plastic piece of the upper left side and don't misspent your money taking this to a shop. With the iFixit tutorial and tools you can do it and save good money.