My MacBook Pro (Early 2011) battery was showing a "Service Battery" indicator. I tried a few solutions to repair it via software but finally decided to go ahead and replace the battery once I saw how easy it was (in the ifixit guide).
Amazingly easy. Step by step via the guide, no problems.
The only thing I missed was the fact that I needed the Y tool. So, after opening the case, I realized that I needed the tool. Once I got the proper tool, it was very easy.