How to Clean Car Battery Corrosion Safely (8 Simple Steps)

What Causes Battery Corrosion?

Most car batteries are lead-acid batteries filled with sulfuric acid. As the battery charges and discharges, it releases small amounts of hydrogen gas and acid vapor through its vents. When that vapor meets the metal terminals and the air around them, it reacts and leaves a crusty deposit behind.

The color of the crust tells you a little about it:

• White or grey powder is usually lead sulfate, which forms on the lead terminal posts.
• Blue or green crust is usually copper sulfate, which forms when the acid reacts with copper cable clamps.

A few things make corrosion build up faster:

• Age. Older batteries vent more as their seals wear out.
• Heat. High under-hood temperatures speed up venting and evaporation.
• Overcharging. A faulty alternator or voltage regulator can push too much current into the battery.
• Loose connections. A loose clamp lets air and moisture into the joint.
• Leaks or cracks. Physical damage lets acid seep out directly.

A light dusting is normal over time. Heavy corrosion that returns within weeks of cleaning is a warning sign that something else needs checking.

What You'll Need

• Rubber or nitrile gloves and safety glasses
• Baking soda and a cup of warm water
• A battery terminal brush or stiff wire brush (an old toothbrush works for light corrosion)
• A wrench, usually 8 mm, 10 mm or 13 mm, for the terminal clamps
• Clean rags or paper towels
• Petroleum jelly, dielectric grease, or a battery anti-corrosion spray

How to Clean Car Battery Corrosion Safely: 8 Steps

1. Gear Up and Park Safely

Park on a flat surface, switch the engine off, and take the key out of the ignition. Let the engine cool for a few minutes. Put on your gloves and safety glasses before you touch anything, because battery corrosion contains dried acid that can irritate skin and seriously hurt your eyes. Keep sparks, flames and cigarettes well away, since batteries can vent hydrogen gas.

2. Inspect the Battery Before You Clean It

Look at the battery case closely. If you see cracks, a swollen or bulging case, or liquid leaking from the battery, stop here. Cleaning will not fix a damaged battery, and it needs to be replaced by a professional. If the case looks healthy and the problem is only crust on the terminals, carry on.

3. Disconnect the Negative Cable First

Loosen the nut on the negative (–) terminal, usually marked with a black cover or a minus sign, and pull the clamp off. Then do the same for the positive (+) terminal, usually red. Removing the negative first stops your wrench from creating a short circuit if it touches metal on the car. Tuck both cables to the side so they cannot spring back onto the posts.

Note: disconnecting the battery may reset your radio presets, clock, or trip computer.

4. Mix a Baking Soda Cleaning Solution

Stir about 1 tablespoon of baking soda into 1 cup of warm water. Baking soda is a mild base, so it neutralizes the acid in the corrosion and makes it safe to scrub away. This is the simplest and safest way to clean battery terminals with baking soda, and it works for most cases.

5. Apply the Solution and Scrub

Pour or brush a small amount of the solution onto the terminals and clamps. You will see it fizz, which means it is neutralizing the acid. Scrub the posts and the inside of each clamp with your terminal brush until you see bare, shiny metal. Work slowly and keep the solution away from the vent caps on top of the battery.

6. Rinse and Dry Completely

Wipe or rinse the area with a small amount of clean water to remove the baking soda residue. Do not hose down the engine bay. Then dry the posts, clamps and battery top thoroughly with a clean rag. Any moisture left behind will help corrosion come back faster.

7. Protect the Terminals

Coat each post and clamp with a thin layer of petroleum jelly, dielectric grease, or a battery anti-corrosion spray. This seals the metal from air and acid vapor. For extra protection, fit felt anti-corrosion washers over the posts before you reconnect the clamps. They are cheap and available at most auto parts stores.

8. Reconnect Positive First, Then Negative, and Test

Reattach the positive (+) clamp first and tighten it, then the negative (–) clamp. Wiggle each one by hand; it should not move. Start the car to confirm it fires up normally. Throw away the used rags safely, since they may still carry traces of acid, and wash your hands even if you wore gloves.

Common Mistakes to Avoid

• Using cola instead of baking soda. Cola can loosen corrosion, but it leaves a sticky sugar film that attracts dirt and moisture. Baking soda and water does the job better.
• Touching both terminals with a metal tool. A wrench that bridges the positive and negative posts can spark, burn you, or damage the electrical system.
• Removing the positive cable first. Always disconnect negative first and reconnect it last.
• Letting liquid into the battery cells. Baking soda inside the battery neutralizes the acid it needs to work and can ruin it.
• Over-tightening the clamps. Tighten until the clamp does not move by hand. Cranking hard can crack the post or strip the clamp.
• Ignoring corrosion that keeps coming back. Rapid regrowth often points to overcharging, a leaking battery, or a battery near the end of its life. Have the charging system tested.

Battery Still Dead After Cleaning? Get Help Fast

Corroded battery terminals block the flow of power, so a car that only clicks or cranks slowly will often start normally once the posts are clean. If you hear a clicking noise but your car won't start, dirty terminals are one of the first things to check.

But if the battery has already drained flat, cleaning alone will not bring it back. You will need a jump-start, either from a portable jump starter or from a professional.

If you are stuck in a parking lot, on the roadside, or in your driveway on a cold morning, Tow-Tow's battery boost service sends a certified technician to you 24/7. Every boost includes a free on-site battery test, so you will know right away whether your battery just needed a charge or is due for replacement. You see and approve the price before anyone is dispatched.

Frequently Asked Questions