There are any number of methods out there for cleaning copper contacts, but some of them are safer than others. Here’s my favorite method to thoroughly and safely clean copper contacts. It’s very thorough, safe, and cheap.
Many people start out with abrasives like fine sandpaper, a scouring bad, or metal polish. The problem with these is that they cause unnecessary wear. They certainly work, but they abrade away metal along with the dirt and corrosion.
There is, however, a safe, effective, and cheap abrasive you can use on copper contacts. There’s a good chance you already have it. Use a U.S. dollar bill.
It just happens that a U.S. dollar bill is abrasive enough to remove the dirt and corrosion, but abrade away little or no metal. Just fold up the dollar bill and rub it over the contacts just like you would use sandpaper. It won’t be nearly as fast as sandpaper of course, because the grit is so much finer. But with some patience, you can sand away all of the corrosion and most of the dirt with the dollar bill. And as long as the two serial numbers remain readable, you can put the bill back in your wallet and spend it.
You don’t have to remove all of the dirt with the dollar bill. To finish the job, use a bit of plastic-safe contact cleaner. Spray the contact cleaner on the contacts, then scrub them with a cotton swab. In a pinch you can use rubbing alcohol instead, but the contact cleaner will be more thorough.
If you want, you can alternate between the dollar bill and contact cleaner too. You can clean the dirt off with the contact cleaner, then scrub off the corrosion with the bill, then repeat the contact cleaner to get rid of any dirt that might remain. Once you scrub with the bill and no more dirt comes onto the bill, you can rest assured it’s pretty clean.
The contact cleaner is flammable, so be sure to let it dry for a few minutes before use. Five minutes is probably sufficient; 30 minutes is better. After you use the combination of the dollar bill and a liquid cleaner for cleaning copper contacts, those contacts will look and work as good as new.