After only two years the battery died on me, without any warning. I woke up a morning and could start my mac - no battery. Plugged to the power, I saw that the battery icon was showing a cross as if I had no battery at all.
Repair went pretty well. It was really easy, once you have the correct tools. Took me about ten minutes (longest part is removing all the screws and putting them back on).
The guide is pretty straightforward, no particular advice.