What Cause Car Battery Terminal Corrosion?

There are several factors to cause your auto battery corrosion.

The most common batteries used in cars are lead-acid batteries. With this type of battery, corrosion is normal. But, what causes car battery corrosion? Today this is the topic of my treatise. It is something unavoidable in lead-acid batteries, and a small amount of it will not really harm your battery. But, knowing what causes it and the ways to prevent a heavy build-up of it, which is what really inflict damage to your battery, is useful information.

What are the causes of car battery corrosion? Actually, there are several factors that cause corrosion, but the main cause of corrosion is the interaction between the hydrogen gas released by the acid in the electrolyte in the battery with the materials in the atmosphere that surrounds the battery.

Corrosion is usually found on the base of the battery terminals and sometimes spread on top of the battery and the terminal cables. It is formed when the sulfuric acid in the battery emits fumes released through the battery vents and the fumes combine with the particulate matters in the air. Corrosion builds up on electrical connections such as the battery terminals.

Corrosion is normal on lead-acid batteries. However, even a small amount of corrosion could restrict the effective delivery of power from the battery to the engine of the car and its electrical system. Which is why there is a need to remove the corrosive material once it is detected.

It is when the build-up becomes excessive that is a cause for real worry. It usually indicates that the battery is impaired or not in good condition. This time, you will need the help of a mechanic to test your battery and remedy the condition, if it still can be remedied. Otherwise, you might need to replace your battery.

Factors That Cause Corrosion

1.Electrolyte leakage

Electrolyte could leak out of a battery because of loose terminal caps or a crack in the battery casing. When the electrolyte leaks because the terminal caps are not properly tightened, it flows out to the base of the terminals where the corrosion is formed.

Cracks in the battery casing can cause the electrolyte to exit via the crack, In such a case, a corrosion build-up can be found on the casing surrounding the crack.

2. Electrolyte overflow

The battery’s electrolyte in a wet or flooded lead-acid battery needs to be topped with distilled water regularly since the water evaporates during a battery’s normal operation. In the process of topping off, there could be times when the water overflows out of the vents to the terminals. This too can cause corrosion.

3. Overcharging

Overcharging a battery generates heat and can heat the electrolyte to boiling point. When electrolyte bubbles, there is an increase in volume and steam rises. When this happens, the electrolyte and the gases could escape from the vents or from a crack in the battery. This is true for both wet or flooded and sealed lead-acid battery. Usually, corrosion caused by overcharging is found on the positive terminal.

Overcharging could be a result of a bad cell. This can cause a decrease in voltage so that the alternator continues to charge the battery to compensate for the loss. As the alternator tries harder to charge the battery, overcharging can result and more than normal hydrogen gas is released. Such a condition can also be the result of a faulty alternator.

4. Undercharging

Undercharging is another factor that can bring about corrosion. Undercharging happens when you use your car mainly for short trips and you have a load of power-hungry electronic devices on your car that draw a large amount of current. If you only drive short trips, the battery is not adequately recharged by the alternator.

Undercharging can also be the result of a damaged voltage regulator. When corrosion is on the negative terminal, it is the result of undercharging.

5. Copper sulfate

Copper sulfate is formed when the copper clamps that are typically used to connect the terminals to the cables corrode. Copper in the clamps are not reactive by itself, but the electricity passing through it and its reaction to the lead in the battery plus the sulfur in the electrolyte cause it to corrode.

6. Age

Batteries, like people, lose its effectivity as it ages. Most batteries are given a lifespan of three to five years. After the third year, you might already be seeing signs that your battery is aging. Corrosion is one such sign.

Effect Of Corrosion On A Car Battery

Corrosion is common on lead-acid batteries, the kind of battery used in almost all vehicles. It is the product of normal usage. A small amount of it should not be worrisome but still needs to be removed. It limits the amount of power delivered by the battery to the car’s engine and its electrical system since corrosion is a poor electricity conductor.

When the battery terminals are corroded, you might find yourself not being able to start your car. The battery can be revived by jump starting it, but having to jump-start your battery often is bad for your alternator. In the long run, corrosion could shorten the life of your battery.

Excessive build-up of corrosion, especially on the negative terminal is real bad news. This may not just be corrosion, but a result of sulfation.

Sulfation is when lead sulfates form on the pores and surface of the active material in the lead plates of a battery, usually caused by undercharging.

Lead sulfates are tiny sulfate crystals that are formed as the battery is being used. Again, a small amount of it is normal and not damaging. Recharging the battery could reverse the process of sulfation.

It is when the battery is frequently undercharged that these lead sulfates are converted into large crystalline deposits. These large crystals that settle on the negative plates diminish the active materials in the battery, discharges it, and causes it to lose its capacity and could render it inoperable.

Recharging the battery with hardened lead sulfate crystals won’t break down the hardened crystals and correct the condition. You might need to replace your battery.

Getting Rid Of Corrosion

Normal corrosion is easy to get rid of. All it needs is a thorough cleaning. Let me show you how.

First, you will need the following tools and materials:

● A stiff wire brush
● Baking soda
● Clean rags
● Socket wrench
● Petroleum jelly
● A pail of water ( if you have no running water or faucet close by)

Also, for your own protection, you will need to wear a pair of safety goggles, rubber gloves, shirt with long sleeves and footwear that cover the toes. Keep in mind that you are working with a hazardous substance here, The electrolyte of a battery contains sulfuric acid that can burn you or even cause a fire.

Here’s the step-by-step way to remove corrosion from your battery:

Step 1 – Locate the battery

Before you can work on it, you must first find your battery. In many of the cars, the battery can be found under the hood. There are, however, cars where the battery is located behind the wheel well, under the floorboard or even in the car’s trunk.

Step 2 – Disconnect the battery terminals

With the socket wrench, loosen the nut on the cap of the post of the negative terminal. Once the caps have been loosened, lift it off from the post. Take note; disconnect the negative terminal first.

Repeat the process with the positive terminal.

Step 3 – Brush off the corrosion

Sprinkle the top of the battery surrounding the terminal posts with baking soda and a little water and start brushing off the corrosion with the stiff wire brush. Do the same with the battery posts, cap, and the cables. Scrub vigorously to make sure that all the gunk is removed.

Step 4 – Rinse with water

After brushing off the corrosion, rinse everything with water, but see to it that not a speck of the gunk and water get inside the battery terminal. You might be compounding your problem if this happens.

Step 5 – Wipe dry with a clean rag

With the clean rag, wipe dry the surface of the battery casing, the caps, cables, and terminal posts.

Step 6 – Apply Petroleum Jelly

Once everything is dry, apply Petroleum Jelly on the caps, terminal posts, and cables. This will help fend off corrosion in the future.

Step 7 – Reconnect the terminals

This time, start with the positive terminal. Put back the nut that fastens the cap on the positive terminal. Tighten the nut, first with your hands, then with the socket wrench. See to it that the cap is tightly secured to the post.

Repeat the process for the negative terminal.

How To Ward Off Corrosion

As has been said earlier, corrosion is normal in lead-acid batteries. However, there are ways to ward it off or prevent excessive build-up of this gunk. Here are some of the things you can do to ward off corrosion.

● Rubbing the terminal posts and caps with Petroleum Jelly or grease, as what has been done after the corrosion clean up, is one way of preventing future build-up of corrosion.
● Apply anti-corrosion products such as an anti-corrosion gel, spray battery protector or felt terminal protectors.
● Always make sure that the battery is kept in a dry place. Moisture contributes to the development of corrosion.
● The inside of the car engine bay should never be washed with water because it can promote rust on the unpainted parts.
● Use clamps made of superior quality copper.


What causes battery corrosion is the reaction between the hydrogen gas released by the acid in the electrolyte with the materials in the air that surrounds it. This is the main cause brought about by several factors.

Normal corrosion is not to be stressed about but still needs to be attended to. What should be prevented is an excessive build-up of this white-blue gunk. This could eventually lead to more serious problems that could shorten the life of your battery.