On re-assembly, you may have trouble getting the top circuit board and shoulder button support structure to snap into place. It’s easiest to get the circuit board around the right analog stick hole, and push it all the way down until it is in place, then to secure the shoulder button support structure.
Make sure the “Home” button clear plastic light spreader (a clear irregular circle-shaped piece) is in place on top of the home button assembly, or it will give the home button a “sunken” appearance.
@mrmacfixit you must have. If it's the same voltage as the old battery, it will work, but you DON'T want to risk puncturing it forcing it into the case.
Maybe the metal is bent, or the plastic on the top of the unit is somehow stuck. I'd look for a bend or disfigured metal, though.