My wife's MacBook Pro's battery died after 2 years use, which came as a surprise to me, as I have an old iBook from 2004 with its original battery still working just fine. (OK, I very seldom used it during the last 5 years, still it's a longer battery life than the MacBook Pro's.
Replacing the battery was very simple, after having read the guides available on iFixit.
I made a note/suggestion at the guide, though, 'cause at first read it seemed that removing the battery charging cable was optional, which is not. Clearing that up the whole swap went smooth and quickly.
Yes, I strongly suggest that check thoroughly the type of battery you need to replace. A lot of places I tried to buy a battery only listed the computer model. It's _not_ enough. There are more battery types only for MacBook Pro 5" than I imagined, and I had the bad luck to order the wrong type locally (in Sweden), following the encouraging info "…it fits the MacBook Pro 5" Early/Late 2011…" (which is exactly my wife's MBP). It was a completely different type of battery, and had to send it back. Then I returned to this oasis of good and correct information and bought the right battery.
And my wife's MBP lives and healthy.
A happy Ending. :)