Quick answer
Wear gloves and safety glasses, disconnect the negative terminal first and then the positive, and scrub the white, blue or green deposits off the posts and clamps with a battery terminal brush. A solution of bicarbonate of soda (bicarb) and water helps neutralise acid residue. Rinse with a little clean water, dry everything, reconnect positive first and negative last, then protect the terminals with a terminal spray or grease. If the corrosion keeps coming back, have the battery and charging system checked.
Is this a DIY job?
- Difficulty: Easy
- Time: 15 to 30 minutes
- Tools: battery terminal brush (or a stiff wire brush), spanner (often 10 mm), bicarb soda, water, old toothbrush, rags, gloves, safety glasses
- Skills: basic hand tools
Step by step
- Protect yourself. Wear gloves and safety glasses. The deposits contain acid residue. Take off rings and metal watch bands.
- Check your manual. Note any radio code or reset steps, and whether your car needs special care when the battery is disconnected. (see How do I replace a car battery?)
- Switch everything off. Ignition off, key out.
- Disconnect the negative (−) terminal first, then the positive (+). Tuck the clamps away from the posts.
- Mix a cleaning solution. About a tablespoon of bicarb soda in a cup of warm water is a common home mix.
- Scrub the clamps and posts. Dip the brush in the solution and scrub. Fizzing means the bicarb is reacting with acid residue; keep applying until the fizzing stops, which tells you the acid has been neutralised. Use the terminal brush’s post end on the battery posts and the clamp end inside the clamps. If the battery has removable vent caps, make sure they’re fitted tightly first, and don’t let solution run into the cells.
- Rinse and dry. Wipe with a rag dampened in clean water, then dry thoroughly. Keep runoff away from paint and wiring where you can, and rinse any splashes off the paint.
- Check the cables. Pull back the boot on each clamp. If the copper under the insulation is green or the cable is stiff and swollen, the corrosion has spread up the cable and the cable or clamp should be replaced.
- Reconnect positive (+) first, then negative (−) last. Tighten firmly, but don’t over-tighten soft lead posts.
- Protect the terminals. Spray with terminal protector or apply a thin coat of terminal grease.
- Start and check. Start the car and check for warning lights. Reset radio, clock and windows if needed.
Why bicarb soda works
Most terminal corrosion on a lead-acid battery comes from battery acid getting out. When a battery is overcharged or runs hot, the acid inside can boil and vent, and the acid that escapes settles on the terminals and clamps and eats into them. Bicarb soda is a mild alkali. It reacts with the acid residue and turns it into harmless salts, water and carbon dioxide (the fizz), so the residue is inert and can be wiped and rinsed away safely. Scrubbing alone moves the acid around; bicarb neutralises it.
If the battery has boiled acid out, cleaning fixes the symptom, not the cause. Have the charging system checked, because a high charging voltage will keep boiling the battery.
Specs table
What the corrosion is telling you
| What you see | What it usually means |
|---|---|
| Light white or grey powder | Normal minor corrosion from acid vapour; clean and protect |
| Heavy build-up that keeps returning | Battery venting or leaking; possible overcharging; get battery and charging tested |
| Green corrosion on clamps and up the cable | Copper corrosion; clean and check whether the cable or clamp needs replacing |
| Wet or crusty battery case, swelling | Leaking or failing battery: replace it |
| Corrosion and slow cranking or flickering lights | Corrosion is likely causing a poor connection |
What you’ll need
- battery terminal brush
- battery terminal protector spray or terminal grease
- battery terminal clamp (if a clamp is damaged)
- battery cable (if corrosion has spread up the cable)
- safety glasses and nitrile gloves
When to call an auto electrician
- Corrosion has spread under the cable insulation, or cables are swollen or brittle.
- Corrosion comes back quickly. The battery may be leaking, or the charging voltage may be too high. (see How do I know if my alternator needs replacing?)
- The battery case is swollen, cracked or wet, or smells of rotten eggs.
- Your car needs battery registration or has a battery sensor on the negative terminal that might be damaged.
Need an auto electrician? Find local auto electricians and mobile services in your city.
Related questions
Q: Can I clean battery terminals without disconnecting them? A: It’s safer to disconnect them. A brush or spanner bridging the positive terminal to metal can cause a dangerous short. Disconnecting also lets you clean the contact surfaces properly.
Q: Can I use Coca-Cola to clean battery terminals? A: It’s a popular trick, but it leaves sticky residue. Bicarb soda and water neutralise acid and rinse off cleanly.
Q: What causes battery terminal corrosion? A: Battery acid escaping and reacting with the metal posts and clamps. A little acid vapour causes light corrosion; heavy corrosion usually means the battery has been overcharged or overheated and boiled acid out. A leaking case or loose terminals can make it worse.
Q: Will corroded terminals stop my car starting? A: Yes. Corrosion adds resistance, which can cause slow cranking, clicking or no start at all. (see Is it my starter motor or my battery?)
Sources
- RACV, “Car battery replacement” – battery management systems and registration on some vehicles. https://racv.com.au/on-the-road/roadside-assistance/car-battery-replacement.html (checked October 2026)
- Planet Ark, Recycling Near You, “Recycling lead-acid batteries” – lead-acid batteries are hazardous; disposal guidance. https://recyclingnearyou.com.au/car-batteries (checked October 2026)
- Rolls Battery, “Cleaning – batteries and terminals” – baking soda and water solution for cleaning, vent caps closed first, rinse with water, wire-brush terminals and re-apply protective grease. https://support.rollsbattery.com/en/support/solutions/articles/646-cleaning-batteries-terminals (checked October 2026)
- Technical review, Ozautoelectrics (October 2026) – bicarb soda reacts with acid residue from batteries that have boiled acid out, neutralising it so it no longer corrodes the terminals. Consistent with standard acid–base chemistry (sodium bicarbonate + sulphuric acid → sodium sulphate, water and carbon dioxide).