How to Clean Battery Corrosion
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That white, green, or bluish crust on your battery terminals is corrosion — dried acid salts — and enough of it can cause slow cranking, charging problems, and no-starts. Cleaning it takes 20 minutes, a box of baking soda, and a wire brush.
Corrosion residue is acidic and irritates skin and eyes — wear gloves and eye protection, don't touch your face, and wash your hands afterward. Keep baking soda solution out of the battery's vent caps (on serviceable batteries); it neutralizes the electrolyte inside.
What you'll need
- Baking soda and water (about 1 tablespoon per cup)
- Wire brush or battery terminal brush
- Wrench for the terminal clamps (usually 10mm)
- Gloves and eye protection (the crust is acidic)
- Terminal protectant spray or petroleum jelly
- Old toothbrush and rags
The steps
Tap through one step at a time — built for one-handed use at the roadside — or switch to all 7 steps to read ahead or print.
Step 1 of 7: Engine off, keys out, gear on
Step 1: Engine off, keys out, gear on
Park, switch everything off, and let the engine cool if it was running. Gloves and eye protection on — you'll be handling acidic residue. Take off metal rings and watches before you go near the terminals.
A battery vents hydrogen gas, which is explosive. No smoking, flames, or sparks over an open battery — and keep the wire brush away from the terminals until both clamps are off.
Step 2: Disconnect negative first, then positive
Remove the negative (−, black) clamp first and tuck it aside, then the positive (+, red) clamp. Inspect the cables while they're off: green fuzz wicking up inside the insulation means the cable may need replacing.
Negative off first, always. With the negative still attached, a wrench slipping off the positive terminal onto any body metal shorts the battery through your tool — sparks, a burned hand, and damaged electronics.
Step 3: Mix and apply the baking soda solution
Stir about a tablespoon of baking soda into a cup of warm water. Pour or brush it over the corroded terminals and clamps. It will fizz — that's the soda neutralizing the acid. Let it work for a couple of minutes on heavy buildup.
Step 4: Scrub with a wire brush
Scrub the posts and the inside of the clamps until both are down to bright, dull metal. A dedicated terminal brush (the kind with male and female ends) does the best job inside the clamps; an old toothbrush handles the corners.
Step 5: Rinse and dry completely
Rinse with a small amount of clean water — or wipe with a damp rag — then dry everything thoroughly with a rag. Moisture left on the terminals invites the corrosion straight back.
Step 6: Apply corrosion protectant
Coat the posts with terminal protectant spray, a felt anti-corrosion washer, or a thin smear of petroleum jelly. This barrier slows the acid vapor that causes corrosion in the first place.
Step 7: Reconnect positive first, negative last
Attach the positive (+) clamp, then the negative (−), and tighten both so they can't twist by hand. Start the car — cranking should be noticeably brisker if corrosion was the culprit. If corrosion returns within weeks, have the charging system checked: overcharging boils the electrolyte and causes recurring buildup.
Reconnection is the mirror of removal: positive on first, negative last. Fitting the negative first puts a live positive terminal one slipped wrench away from a direct short.