Replace Battery in Mac Book Pro
5 - 10 Minuten
my Battery was 2 years old and had over 1000 cycles with only about 50% health it only got me an hour of normal use with the battery
Easy, I think that's all that needs to be said
You should press option PR when you start your computer again with your new battery. I suspect this is how they would do it at the mac store if you brought it in there. It resets the NVRam which forces the computer to read the battery, and it will see its a new battery. Wouldn't hurt to also fully charge it then let it recharge all the way and recharge all the way, even though it may not be necessary.