What do you use to clean the coil in the battery compartment?

Google exists.

But to answer your question, the white powder is alkali. Put on rubber gloves and swab the powder away with Q-tips dipped in vinegar (to counteract the base). Then dry the contacts and hope for the best. If the corrosion isn’t too bad, it should be fine.

Coils? Are you talking about terminals and posts? Remove the cables. Rubber gloves wielding steel wool. SOS pads work beautifully.

You can use detergent or baking soda and hot water to dissolve and neutralize the corrosion (that white powdery stuff) on the coil. Use an old tooth brush to scrub it away. Rinse with clean water and dry completely. You could then apply a bit of dielectric compound (available at any auto parts store) to prevent further corrosion. Don’t get any of the white powder on your clothes or hands. (It will burn you.) If you do, apply the baking soda/detergent mixture to the spot immediately, or launder the clothing immediately. Wear eye protection.

Before doing anything be sure to put on rubber gloves so you don’t get anything on your skin or you might get burned. Protective glasses might be a good idea as well. After that, it depends on how long the corrosion has been there. A tiny bit of baking soda followed by a tiny bit of vinegar should foam sufficiently to neutralize any residue. Then use a cotton swab to dry off the connection. If you’re lucky it will go back to working with a brand new battery. You might discover that it was too late to be saved. I tend to chalk it up to being destroyed and tossing it in the trash foregoing the hassle

Alright. I’ll come back to this. Thanks.