How do I remove the negative terminal nut/adapter?

Tapy’ Tap Tap :)

No problem, in general Oxidization on copper/lead/steel battery terminals is surface cosmetic, if left for say 10 years, then it could get a ‘little’ destructive, but really just some helpful taps with a hammer, or focused taps using a flat blade screwdriver/hammer where the seams should move.

Next try giving it a good shoot of penetrating oil and leave it for a night - use a good brand like $6 to $15 bucks.

Lastly get some battery contact spray, a good name isn’t coming to me now, but it will look like a deep red when you spray it on, and i mean alllll over the area, saturate it. Then it should last another 5-6 years before replacing the battery.

PS. Gloves and Safety glasses are a REALLY good idea when doing stuff with corroded battery terminals, that stuff sucks in the eyes!

Get a sturdy screwdriver and whack it a few times with the handle. You hold the metal part of the screwdriver and the plastic part is hitting the battery terminal. It’ll knock it loose. Don’t be afraid to jiggle it off…it won’t be easy, but you are not going to hurt the battery or the terminal.