Mac Book Pro from 9 years ago is now good as new!
I still had the factory battery in my MacBook Pro. I bought it in 2009 so the battery was definitely at end of life. It would only stay charged for a half hour if it was off the charger.
Great! Super easy. I did watch a Youtube video to make sure I was doing it correctly, but most could do the switch out without help.
In the Youtube video, calibration of the battery was recommended. After replacing the computer with the new battery, charge up the battery fully, then leave the computer on until dead. This process took awhile. Then charge the battery fully again. Everything works great.