Battery acid is corrosive. Wear safety glasses and rubber/latex gloves throughout this process. Keep sparks and flames away from the battery at all times, batteries emit hydrogen gas during charging.
What Causes Battery Corrosion?
Battery terminals corrode over time due to hydrogen gas released from the battery reacting with the air. White, blue, or green deposits form around the terminal connections. This crusty build-up increases electrical resistance, meaning less current reaches the starter motor, causing slow starts, clicking sounds, or complete failure to start.
What You'll Need
- 8–10mm spanner or socket
- Wire brush or old toothbrush
- 1 tablespoon bicarbonate of soda (baking soda)
- 1 cup warm water
- Safety glasses
- Rubber gloves
- Clean cloths
- Petroleum jelly (Vaseline) or terminal grease
Step-by-Step
- Turn off the engine and remove the key.
- Disconnect the negative (−) terminal first. Loosen the clamp bolt with the spanner and twist and pull the cable off. Always disconnect negative first to reduce the risk of a short circuit.
- Disconnect the positive (+) terminal in the same way.
- Mix 1 tablespoon of baking soda in 1 cup of warm water.
- Pour or brush the solution onto the corroded terminals. It will fizz, this is normal. The fizzing reaction neutralises the acid in the corrosion.
- Scrub with the wire brush or toothbrush to remove the loosened deposits.
- Rinse with a little clean water and dry thoroughly with a cloth.
- Apply a small amount of petroleum jelly (Vaseline) to both terminals. This seals them from moisture and slows future corrosion.
- Reconnect the positive (+) terminal first, then the negative (−). Tighten the clamp bolts firmly.
After Cleaning
Start the engine and check it fires up normally. If starting is still slow or unreliable, the battery may be reaching the end of its life (typically 3–5 years). Most garages and tyre centres will test a battery for free.
Prevention: Apply terminal grease or Vaseline after every reconnection to slow the build-up of corrosion.