Great help from iFixit to change a battery on a MBP...
I had to change to battery of this MacBook Pro 15" Unibody (Early 2011/Late 2011/Mid 2012), because after only 15 cycles, the battery wasn't responding anymore. Apple and some resellers were asking me for 220 to 250€ for this and would have taken my MBP for at least 2 weeks. With iFixit, I did it in 5 minutes, for only around 120€ (screwdrivers and spudger included)...
I followed exactly the handsome user guide provided buy iFixit concerning this precise model of MBP (MacBook Pro 15" Unibody Early 2011 Battery Replacement). And I did everything in 5 minutes, without having any problem. The job was very easy, and anybody can do it, unless you have the right tools of course, that I also ordered to iFixit. Even a little kid could do the job. So do not hesitate doing it yourself...
No particular advice, except the fact that you must have the right tools and a clean table to do it, of course.
By the way, I do think that if the precise screwdrivers are essential, the spudger can be certainly easily replaced by any kind of plastic thin flat tool you may have at hand.
PS: forgive me for my awful English and have a lovely day.
Phillips #00 Screwdriver
Tri-point Y1 Screwdriver
MacBook Pro 15" Unibody (Early 2011-Mid 2012) Replacement Battery