My MacBook pro 2009 model battery had only the capacity to keep the macbook up and running for ~45 minutes. A new battery was required (as my daily train travels from and to work takes 50 minutes :).
It couldn't be easier. Ordered a battery.. opened my macbook.. and discovered pentalobe screws. A short search on ifixit delivered the solution as they are (as far as I can see) the only ones that can supply this screwdriver. I'm from the Netherlans, ordered it via ifixit, opted for the longest (and cheapest) delivery method (2-3 weeks) and was suppressed to see it to arrive within 1 week !!!
The advice? Well, visit ifixit.com, get the manual and the gear and your all set to go.