Safety first. Wear eye protection and gloves. Keep sparks, flames and cigarettes away: lead-acid batteries can release hydrogen gas. Disconnect the negative (-) terminal first and reconnect it last. Never work on hybrid or EV high-voltage batteries. Follow your owner’s manual.
Corrosion on the terminals can make a healthy battery act dead. Cleaning it is cheaper than a new battery, so do it before you check the cost of replacement.
What you will need
- Gloves and eye protection.
- Baking soda, water and an old brush, or a terminal cleaning brush.
- Spanners to loosen the clamps.
- Terminal protector or grease.
Steps
-
Switch everything off. Disconnect the negative (-) cable first, then the positive (+).
-
Mix a spoonful of baking soda in a little water and brush it onto the corrosion. It will fizz.
-
Scrub the terminals and clamps until clean metal shows.
-
Wipe with a damp cloth and dry thoroughly.
-
Reconnect positive (+) first, then negative (-) last. Tighten so nothing moves.
-
Apply a thin coat of terminal protector.
Troubleshooting
- Corrosion comes back fast: the battery may be leaking or overcharged. Check charging voltage.
- Cracked case or swollen sides: replace the battery.
What is that crust on my battery?
The white, blue or green powder around terminals is corrosion from small amounts of acid vapour and gas reacting with the metal. It is a poor conductor, so it can restrict current and make a good battery behave like a bad one. Heavy corrosion can also mean the battery is leaking or being overcharged, so look at the cause as well as the symptom.
Prevention
- Keep terminals tight and the battery secured.
- Apply a thin coat of terminal protector or grease after cleaning.
- Replace cracked or damaged cable ends.
- Check the charging voltage with the voltage checker; consistently high charging can accelerate corrosion.
- Keep the top of the battery clean and dry.
Cleaning safely
Baking soda neutralises acid but will fizz. Do not let the mix get into the battery cells. Rinse with a small amount of water and dry thoroughly. Dispose of used rags carefully because they contain residue. Wear gloves and eye protection throughout, and remove metal jewellery.
When cleaning is not enough
If the cable ends are eaten away, replacement cable ends or a new cable may be needed. If the terminal posts themselves are damaged, replace the battery. If the case is cracked or swollen, stop and replace it. A parts store can test the battery for free in many cases, and our replacement cost calculator shows what a new one will cost.
Related checks
- Is the battery old? See how long car batteries last.
- Still not starting? Try the dead battery or alternator checker.
- Want to test it? Follow how to test a car battery.