Why Your Car Battery Is Corroding (And How To Fix It)

If you’re like many people, you don’t lift the hood of your car unless you really have to. If the car is working well, that means it could be years before you get a look at what’s underneath. That includes the battery terminals, which can develop a coating of bluish-white corrosion during that time.

A corroded battery will still start your car—at least until the corrosion gets bad enough to interfere with the electrical connection. If that happens, you might get stuck on a country road in the middle of winter, and if you’re not the type who carries tools in the car, you could find yourself waiting in the cold for roadside assistance without the ability to start your car to stay warm.

Why do batteries corrode, what does corrosion mean about the state of your vehicle, and how can you prevent it? With the help of automotive repair experts, this post answers these questions.

What Causes Battery Corrosion?

Standard automobile batteries (not the sealed, maintenance-free types) contain a sulfuric acid solution that acts as an electrolyte, and it’s predominantly responsible for any corrosion on the terminals. This acid naturally releases hydrogen gas, which escapes through vent openings to prevent a dangerous hydrogen buildup inside the battery. When this corrosive gas contacts the metal terminals, a chemical reaction takes place that produces the corrosion you see. Moisture and salt in the air speed up the reaction.

This process is unavoidable, which is actually good news in a way. It means that you don’t need to be alarmed if you see corrosion on your battery terminals. However, if you don’t want to get stuck out in the cold, you should remove it and take steps to prevent more from forming.

Causes of Excessive Corrosion

In normal conditions, it takes about three years for battery terminals to develop enough corrosion to need cleaning. If your terminals become noticeably corroded before that time, or if the corrosion is unusually heavy, here are some possible reasons:

Leaking battery

The battery casing could be cracked, allowing the acidic electrolyte to seep out. If the crack is near the terminals, corrosion will build up quickly.

Overheating

Corrosion occurs more quickly at higher temperatures, which means it can build up faster in the summer than in the winter. Excessive corrosion can also be a sign that the car’s cooling system isn’t working properly and the engine is overheating.

Overcharging and Undercharging

When the battery gets overcharged, the electrolyte releases hydrogen gas at a faster rate, producing excessive corrosion on both terminals. This is a sign that the car’s voltage regulator isn’t working properly.

If the battery is undercharged, you’ll probably notice more corrosion on the negative terminal than on the positive one. This happens because the car’s electrical system is drawing too much power.

Old battery

The expected life of a car battery is five to seven years. If you see excessive corrosion (and you can rule out other causes), it’s probable that the battery has reached the end of its service life and can no longer hold a charge. Mechanic Bryan Jewett explains how to test it:

1. Use a multimeter set to DC voltage.
2. Turn off the car.
3. Connect the positive lead to the battery’s positive terminal and the negative lead to the negative terminal.
4. Check the voltage. A healthy, fully charged battery should read between 12.6–12.8 volts. If below 12.4, it likely needs charging, and under 12 volts may indicate it’s not holding a charge well and needs to be replaced.

How to Clean Battery Terminals

Here’s a rundown of the procedure for cleaning corrosion off of battery terminals supplied by Garrett Torelli of Batteries Plus:

1. Put on gloves and eye protection for safety, and open the hood.
2. Use a memory saver: Before disconnecting, plug in a memory saver to avoid losing radio presets, clock settings, and other functions.
3. Disconnect the battery: Starting with the negative terminal, then the positive.
   • Pro tip: Use pliers to hold the bolt steady while unscrewing.
4. Inspect the battery cables: Check for wear or corrosion and replace any damaged cables immediately.
5. Remove and clean the battery: Use a wire brush and neutralizing solution (baking soda and water or terminal cleaner spray) to remove corrosion. Pro tip: Clean the terminal clamps, too.
6. Reinstall the battery: Place it back, secure it, and reconnect in reverse order (positive first).
   • Pro tip: Ensure the clamps are tight to prevent future issues.

How to Prevent Corrosion

This is easy to do: Just coat the terminals with petroleum jelly or a battery terminal protector, a dielectric compound that prevents the corrosion reaction from occurring. It doesn’t hurt to reapply this protection as often as you like, but at least do it when you notice corrosion beginning to form.

FAQ

How often should I check my battery terminals for corrosion?

If your battery is fairly new and you aren’t experiencing problems, you should check for corrosion about once a year. As the battery ages, check more often, especially if the engine has trouble turning over or the headlights dim when you start the car.

Should I consult a professional if I find corrosion?

You can generally handle battery corrosion yourself, but you should bring the car in for service if you notice any of the following:

• Excessive corrosion;
• Significantly more corrosion on the negative terminal than on the positive one;
• A battery leak;
• Overheating engine.

About the Experts

• Bryan Jewett has been in the automotive business for 20 years. He is the owner of Casey’s Automotive, which is based in Virginia.
• Garrett Torelli is the Senior Merchandise Manager at Batteries Plus.

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