Macbook pro 2012 battery disconnect

Replacement depends on the exact sub-model. The 13-inch 2012 non-Retina model was in continuous production until Oct 2016. According to Apple's stated policy they will provide repair parts for five years following the date of last production. For the non-Retina 13, that means Oct 2021. Nice.

I just answered another person's very similar question before seeing your response. As I am the world's most awkward typist, allow me to suggest you see my post in this thread:

Is it possible to get the battery replaced for my MacBook Pro early 2011? If yes where?

I would remove the battery if that model permits (I believe it does). A battery should not smell and, if it does, could indicate that part of it has split open. That causes two things, both horribly bad:

1) The goop inside the battery leaks, destroying the logic board and anything else it touches including the aluminum case.

2) The battery expands taking bending the entire case assembly and rendering the keyboard and trackpad inoperative.

Of course, both could happen. No joy in that either.