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Why Do Car Batteries Corrode? Tips For Saving Your Battery

A car driving down a road. Take care of battery corrosion before it winds up stranding you with a no-start condition.

Why do car batteries corrode? If you’ve ever popped your hood and seen that telltale mix of green-and-white powder on the terminals of your car battery, you’ve most likely wondered about this question.

Since batteries are protected from the elements, how do they suffer from this type of damage? The answer, as with many things corrosion-related, has to do with chemistry. Fortunately, there are a few steps you can take to extend the life of your battery and save yourself from potentially being stranded.

Gas Up

Unlike the rust that affects your vehicle’s sheet metal, the corrosion on your battery terminals isn’t related to road salt. Why do car batteries corrode? It’s usually due to the natural chemical processes going on inside the power pack itself that help it to store electricity.

Most batteries are filled with sulfuric acid, and a by-product of heating or cooling this acid — which happens when the battery is charging or discharging — is that it produces hydrogen gas. That gas has to be vented outside of the battery, and when that happens within the tight confines of your engine bay it can interact with the lead on the battery terminal, causing corrosion.

Battery corrosion

There is another type of corrosive process you might see on your terminals, too, which happens when the copper on the terminal clamp gets wet and reacts with the lead electrode it is connected to. This manifests as a greenish substance on the terminal itself (or white, if the terminal clamps are made of aluminum).

Finally, some batteries corrode because of something called “sulfation.” This occurs when a battery isn’t regularly recharged, either because it’s only being driven for short trips or because it’s getting old. White sulfur crystals form on the negative battery terminal or occasionally around the battery itself if it’s leaking sulfuric acid. They can also cluster around the positive electrode if the alternator is over-charging the battery.

Clean It Up

For the most part, battery corrosion is easy to deal with. A wire brush and some baking soda and water are often the only abrasives you need to scrub off the existing powder that’s caked onto the terminals, electrodes or casing. You can also use felt protectors to help seal the battery terminals themselves.

You’ll want to do this as soon as you see it, because if left too long, sulfation can become permanent. A corroded battery component also conducts less electricity than a clean one, which could eventually lead to starting issues.

Keeping your battery properly charged will help prevent sulfation from occurring, but if you notice negative terminal corrosion on a regular basis, even if you drive long enough for the alternator to do its thing, your battery might be too old to receive a full charge. If you are regularly seeing positive terminal corrosion, it’s time to check for a fault in your charging system to determine why it’s overcharging.

Check out all of the batteries available on NAPA Online or trust one of our 17,000 NAPA AutoCare locations for routine maintenance and repairs. For more information on why car batteries corrode, chat with a knowledgeable expert at your local NAPA AUTO PARTS store.

Photo courtesy of Unsplash.

Benjamin Hunting View All

Having been bitten by the car bug at a young age, I spent my formative years surrounded by Studebakers at car shows across Quebec and the northeastern United States. Over ten years of racing, restoring, and obsessing over automobiles lead me to balance science writing and automotive journalism full time.  I currently contribute as an editor to several online and print automotive publications, and I also write and consult for the pharmaceutical and medical device industry.

One thought on “Why Do Car Batteries Corrode? Tips For Saving Your Battery Leave a comment

  1. I nearly bought a new battery but after reading this I am going to check out my charging system because it is corroded on the positive side not really the negative side. Thank you.

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