With the 2012 at least, the first tell for the battery expanding is actually the trackpad. The trackpad will start to no longer click as well because it is still a physical button in this model. It might not even click at all before it finally swells to the point it shatters the trackpad. Luckily the placement of the battery spares the keyboard too; its all in the palm and trackpad area.
I'm on battery number 2 at this point, and the swap takes as long as a dozen phillips heads takes to unscrew then screw. I don't envy the more recent glued battery models and don't look forward to the day when this pretty repairable rig finally bites the dust and I'm forced into one.
I would replace the battery if that was the only part affected. Unfortunately when it expanded just like the last time it bends/warps the top case and keyboard, the metal around the trackpad and the bottom case. I can't just replace the battery and leave everything else bent/warped, the laptop won't sit level, the screen will not close completely. It's really not a cheap or easy task. Not to mention the risk involved in removing a battery that is expanded and could rupture.
RIP 2015 MBP - you still had a few years left in ya.