What have you used that works best? I just tried some vinegar and also read you can use alcohol. I would like to clean all my battery connectors.

Eraser if you can reach it, like the flat plate of a deans connector. Or electric contact cleaner sprays that do not harm plastic.

CRC 5103 Quick Dry Electronic Cleaner. You can find it just about any local home improvement or auto store.

ok thanks I seen the sprays ill go that route see what gives

electrical cleaner... in a spray can..
or
Motor cleaner...in a spray can.

or even brake cleaner.. but this might damage plastic housings...

I don't think I've ever "cleaned" any connector in all my years in RCing. Deans, Race Prep, Power Poles, EC5, XT60, 3.5mm/4mm bullets, low profile battery connectors "bird cage"/pronged ...etc. etc. etc. They all are basically self cleaning unless you are submerging them in honey or something. Even had some cheap new EC5 connectors starting to form a weird greenish tarnish on them. After a few connects, and disconnects, the tarnish got swiped away.

Speaking of Tarnish (band I was in):
RustyMe
RustyYou
RustyUs

I would not use brake cleaner. Motor cleaner might be ok, but I wouldn't use that either. Brake cleaner seems to be a common multipurpose cleaner in RC for some silly reason. It is a caustic liquid and will cause pitting of the surface of metals, especially plated metals.

The best thing to use if you need it is either straight isopropyl alcohol in as high a percentage as you can get(ideally no lower than %90), or a cleaner specifically for the purpose such as Caig Deoxit or other electrical contact cleaner.

As an FYI, the WD40 contact cleaner works really well. We use it at work, having switched from CRC (not RC Affiliated) Contact Cleaner

.

I want the original Blue Shower contact / motor cleaner, brought back into production... BEST EVER... EPA banned it.

I've got some stuff called "Rail-Zip". (Pacer) Used to clean train track/rails and contacts. Won't harm plastics. Restores conductivity.

This is all you'll ever need. Industry leaders in electrical contact cleaners. Ask any electronics engineer or technician. You don't need chemicals banned by the EPA. Use the De-oxit Shield after you clean with Deoxit D5 if you run in really harsh environments. Thank me later. https://caig.com/deoxit-d-series/

do you need to clean the bullets? I've never cleaned the bullet sockets in a battery.