Early 2011 15" Macbook Pro battery gave up after almost exactly 2 years and only 128 cycles. :( Not at all impressed with the longevity of the battery included with my original Macbook Pro
The repair was extremely easy. The toolset had everything I needed to do the repair and the battery removal and installation took less than 10 minutes. The online guide shows exactly what you need to do with photos and all. As always, iFixIt is the one stop shop for your needs to do this yourself. Taking it into Apple or a certified workshop (MacStore) takes too long (they want to keep the device until the battery gets it, they won't pre-order it... just silly). There is no reason that anyone that can operate a screwdriver can't do this repair themselves.
Ensure you have a a clean workspace and the right tools (very small phillips screwdriver and a 'twisted' 3 prong end). The Macro Bit Set that iFixIt sells includes it all and just made more sense than buying a couple of the tools individually as it's not that much more expensive. Super easy swap!