What Causes Corrosion on Car Batteries


If you’ve ever jump-started a car, replaced an old car battery, or peeked into your car engine’s bay, you’re very familiar with battery terminals. But, if your vehicle is old, your battery is faulty, or you haven’t maintained your vehicle frequently, you’ve seen the powdery, white and bluish-green substance on the battery terminal. That right there is battery corrosion.

What causes corrosion on car batteries? Why do the colors differ? How does it affect the performance of your vehicle?

If you look at it and think it’s harmless, because all metals corrode as they age, you are not entirely right or wrong. Corroding battery terminals can cause severe problems in your car engine. Very often than not, it could also be the reason why your car has hard starts, battery and engine break down.

The best way to prevent or solve a problem is to know the underlying cause of the problem. And, that’s precisely what this article does for you – tell you what causes corrosion on your battery terminals.

What causes this build-up?

Corrosion on battery terminals is very common and affects mostly vehicles with a lead-acid battery. Many acid batteries are filled with sulphuric acid. As the temperature of your battery alternates between hot and cold, gases escape from the battery through vents on the battery. These gases mix and react with other elements around the battery causing the corrosion you see.

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From the explanation above you’d expect corrosion to form when your vehicle has been sitting idle for months or years, but nope. It doesn’t take long to form. If they don’t take long to form, what could be the reason behind corroding terminals?

6 Reasons for Battery Terminal Corrosion

There are many reasons corrosion forms on the terminals and the corrosion itself differ in appearance, color, and texture, depending on its cause. Here are the top 6 causes of battery corrosion.

1.  Electrolyte Leakage

Though batteries are made to hold the acid in a safe and strong container, leaks are still a possibility. If the electrolyte leaks out and accumulates around the battery terminals due to lack of proper maintenance or damage, then there’ll be corrosion.

Though the chances of this happening with a sealed maintenance-free battery is minimal, it is still possible. For batteries that require constantly topping the electrolyte with water, the probability of spilling some electrolyte onto the terminals is higher. In both cases, the presence of electrolyte around the terminals will cause corrosion.

2. Overfull Battery

Feeding your refillable battery too much water can spell trouble. You need to be careful about only topping the electrolyte up till the highest markers and no further. It’s recommended to top the electrolyte on a cool day to give room for the liquid to expand when the temperature of the battery increases while in use. Since the terminal are made of metals, any excess flowing out of the vents will corrode them.

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3. A chemical reaction in the Copper Clamps

Most quality clamps that connect the battery to the wires are usually made of copper. From the little chemistry we know, copper cannot corrode all by itself. But, in the presence of sulphuric gases from a leaking battery and a little help from the current flowing through the copper clamps, copper sulfate is born, thus causing battery terminal corrosion. It is the bluish-green crystals that form around the terminal.

The chemical reaction looks like this:

Cu (s) + 2 H2SO4 (ℓ) → CuSO4 (aq) + 2 H2O (ℓ) + SO2 (g)

Told you, we know chemistry.

4. Overcharging

They say that too much of everything is bad, charging batteries is not an exception. Surprising but true, overcharging can lead to battery corrosion. It will raise the battery temperature which causes the electrolyte to expand in volume.

And you know the thing about pressure is that it finds a way out, even if the battery is the sealed or flooded kind, the electrolyte will eventually flow out through vents or cracks. In the end, it is the terminal that bear the brunt.

5. Hydrogen gas

The reaction in the battery produces hydrogen gas. There’s some in the air we breathe every day and it is pretty harmless in small quantity. However, as harmless as it seems it can cause corrosion once it reacts with other gases. It usually indicates charging issues; if it forms on the positive terminal it may mean that the battery is overcharging or undercharging if on the negative terminal.

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6. Battery Age

Irrespective of how you maintain your vehicle, if you’ve used the same battery for a period close to 5 years, then you shouldn’t be surprised to see the terminals corrode as the battery’s performance declines. Batteries have a 5-year lifespan, but of course, various factors influence how your age and the first sign of a failing battery will come from your engine’s performance.

Problems Caused by Automotive Battery Corrosion

The most noticeable problem with a battery that’s corroded is the danger of the vehicle not starting when you want it to. Of course, you know that this could happen any time, the most embarrassing being when the light shows green and you want to move, but that’s just the tip of the iceberg.

Your car’s on-board computer can develop issues too and bail on you at any time as a result of the problematic battery. If your battery is leaking, old enough to be replaced, or the corrosion has eaten too deep into the terminals, then you need to get a replacement ASAP.

How to fix it

There is no easy way to get rid of corrosion on your battery terminals, all it needs is thorough cleaning. As expected you’d need a solvent and something tough to scrub with. A wire brush or old toothbrush and battery cleaner will do.

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Baking soda – water solution

You will need some baking soda-water solution to remove copper sulfate that’s accumulated on the terminals. Ensure the car’s ignition is turned off when you’re doing this. Pour the solution on the terminals and give them a good scrub. Once done, flush the solution away with clean water and put back the clamps in their correct position.


Get any soft drink that contains carbonic acid – most of them do. Pour some over the terminal and then remove the residue with a soft sponge. This is a good alternative to baking soda.

Cleaning heavy corrosion

Avoid using force if the corrosion on your battery terminals or copper clamp is tough to remove. What you should do is mix your soda-water solution into a cup and soak the clamps in the cup, you could soak soft towel or tissue paper with the solution and then place the wet towel over the battery terminal. Let it sit for about 20 minutes then inspect for improvements.

How can we prevent corrosion?

There are a couple of ways to prevent the buildup of corrosion on your battery terminals. To keep your battery operating as good as new, you should apply these preventive measures on cleaned or fresh batteries.

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Anti-corrosive sprays

There are numerous anti-corrosive sprays on the market that prevent terminal corrosion. But, if you find these to be too expensive, Vaseline or grease would do a nice job. I’d recommend grease over Vaseline as it’s able to withstand heat.

Battery charging

If your battery is corroding because of overcharging or undercharging, then you should consider taking it to the mechanic to tune the electrical fault. If your vehicle is undercharging because the AC is always running or you have a powerful amplifier, consider making some changes to save your battery.

Copper compression terminals

You could consider these clamps as they are made from tinned copper which ensures that the whole clamp gets into contact with the battery terminal.

Keep up with your vehicle maintenance

Keeping up with your vehicle maintenance schedule as well as following the right car maintenance advice is the best way to avoid corrosion on a car battery. Make sure you are neither underutilizing your battery with only short trips or drawing too much from it by using car gadgets when the engine isn’t running. You can prevent corrosion, or catch it early is you keep your battery in good shape.

Final Thoughts

The most common cause of any problem that your car battery may be giving you is usually the result of gas leaking from the vent. However, your battery may also malfunction if the terminals are loose, the battery case is cracked due to being dropped, or your component speaker is always blaring full force even when the engine is not running.

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A battery that has corrosion on the terminal can be cleaned quickly with simple homemade DIY tools, but implementing these preventive measures could help you stop corrosion before it becomes a problem as well as extending the lifespan of your battery.

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