MacBook Pro 15" Unibody Mid 2010 Logic Board
Mmm, I think in two options:
1. The new battery has some imperfections and don´t met the official dimensions.
2. If the new battery is used, had an overheat and that caused a variation in its dimensions.
Sorry if I can´t help you more
Before start, make a clone of your old HD into the new one, if you don't want to initiate a fresh copy. (Carbon Copy software is good).
If you does not have the spudger, use the Dremel to file a wooden piece
(Chinese stick maybe) to transform in a spatula. Works fine for me