Car Battery Corrosion: What Causes & How to Fix the Problem

Have you ever noticed unusual, white build-ups on battery terminals? That is battery corrosion and can be a sign of issues within the electrical system of your car. Not only does it look nasty, but it can also cause weak contact between battery posts and terminals. If that happens, your battery will not charge as it should, and you may have trouble starting the car in the morning. Not only will a clean battery last longer, but it will also make your vehicle more reliable.

In this article, you will find out how the car battery works and how to fix or prevent battery corrosion.

How to fix corroded car battery.

How Does Car Battery Work?

Any battery operates on a simple principle. A negative battery side, or anode, has an excessive amount of electrons. On the other hand, a positive side, or cathode, lacks electrons. Between them, there is an electrolyte that acts as a barrier that prevents electrons from going directly from negative to positive side. When you connect an appliance to the battery, electrons flow from the negative to the positive side and make it run.

A standard car battery has six cells. Each of them has a mixture of lead plates as anodes and cathodes. Also, there is sulfuric acid that, combined with an insulator plate, acts as an electrolyte. This is the reason we call them lead-acid batteries. Chemical reactions within the battery are reversible, allowing it to both discharges or store the electricity.

When the battery is discharging, acid transforms into water and hydrogen gas. The process goes in the opposite direction during the charge period, with hydrogen and water transforming back to acid. As every cell produces 2 volts, bonding six of them together gives 12 volts.

What Causes Battery Corrosion?

Poor Ventilation and High Temperatures

As the battery charges, it produces hydrogen gas. During that process, any excess pressure escapes through a vent hole at the side. In most cases, this gas goes to the surrounding atmosphere and causes no problems. Still, these fumes can sometimes cause battery corrosion because of poor ventilation and high temperatures under the engine hood.

Fluid Leaks

Unlike escaping hydrogen gases, which are not dangerous, fluid leaks are a different story. The liquid inside the battery called sulphuric acid is harmful. Because of that, the battery casing is completely sealed. However, various mechanical damages can cause cracks and result in leaks. Again, combined with poor ventilation and high temperatures, it causes excessive amounts of hydrogen gases. Also, leaking fluid can cause skin burns, destroy your clothes, and pollutes the environment. Therefore, you must replace a leaking battery without delay.

Bad Battery Terminals

Bad or loose battery terminals will cause poor electrical contact and high temperatures. The difference in temperatures and material expansion between battery posts and housing can allow a certain amount of gasses to escape and come in contact with battery terminals. In addition, resulting corrosion buildup will only make the electrical connection worse. Over time, this could lead to a dead battery, as it will not receive the charge.

Overcharging and Overfilling

Over-filling battery with water will reduce the space for hydrogen gases within the housing, increasing pressure. As a result, excessive fluid will evaporate and escape through a vent hole. Again, this can cause battery corrosion if there is not enough ventilation under the hood. Overcharging the battery has similar effects as overfilling. High voltage increases the temperature within the battery, resulting in excessive hydrogen fumes that can cause corrosion. In most cases, this will happen if the voltage regulator on the alternator fails.

How to Fix a Corroded Car Battery

Despite the nasty look, removing battery corrosion is easy and requires very little skill and tools. In most cases, it will take no more than a suitable wrench, toothbrush, and some baking soda. Also, as always use protective gloves and safety glasses.

1. Remove the Terminal

Battery terminals have bolts and nuts that hold it tight over battery posts. To prevent potential damage to sensitive electronics, start with the negative side.

Using a suitable wrench or a ratchet and socket, loosen up and remove negative battery terminal. Lay it to the side, securing it from touching the battery post or any metal parts.

Next, repeat the procedure on the positive side. Sometimes, you will first need to remove corrosion build-ups with a wire brush. After removing the terminal, give it several gentle taps with a wrench. This will shake off loose corrosion.

2. Prepare the Baking Soda Mixture

The easiest way to remove the build-up is by using baking soda. It neutralizes sulphuric acid and dissolves the build-up.

Start by pouring one or two spoons of baking soda powder into a suitable cup. Next, add a small amount of water to it, just enough to convert the powder into a dense paste. This is a better method than a liquid mixture because you can apply it without making a mess.

3. Apply the Paste on Corroded Parts

Using a dry toothbrush, smear the baking soda paste on corroded parts and leave it for several minutes.

4. Scrub Off Corrosion Build-Ups

Soak the toothbrush in water and start scrubbing the terminal. You will need to repeat this several times until all corrosion is gone.

However, make sure not to use too much water while doing this. When finished, clean off the battery surface to prevent eventual discharge.

5. Inspect the Battery

After removing all traces of corrosion, examine posts and terminals with care. Surfaces where these components meet must be smooth and with no groves or pitting holes.

Also, look for traces of corrosion on battery cables and check the condition of connection points with terminals. Replace the battery terminals if needed.

6. Put Everything Back

With all surfaces and connection points cleaned, refit both battery terminals. Start by attaching and tightening the positive side and then move to the negative side. Check if both terminals are tightly fitted.

How to Prevent Battery Corrosion

After removing the corrosion from your battery, you can use these tips that will prevent it from happening again:

  • Make sure there is a good connection between the battery post and terminal. To achieve this, battery terminals must be in good shape. A terminal should have a clean and smooth surface where it meets the post, and you should be able to tighten it up. If not, replace the battery terminal with a new, high-quality one.
  • Check the battery water level once a month and top it up if needed. Use only distilled water for this purpose and be careful not to overfill the battery. Also, check the charging state of your alternator using a multimeter. In most cases, readings above 15 volts are a sign of a bad voltage regulator.
  • Apply paste coatings and sprays to the battery posts. They will provide an additional layer of protection. An alternative are felt washers, which go between the terminal and the plastic battery surface. These fiber pads are soaked with a special chemical that neutralizes acid fumes.

Different Types of Batteries and Corrosion

Wet cell or flooded batteries are the oldest type and are still most used in cars today. As being most spread, they come in a wide range of sizes and capacities. These batteries use lead plates and a sulfuric acid electrolyte. Also, they have plate separators. Wet cell batteries require maintenance, as a certain amount of electrolyte will vent to the atmosphere with time. Also, these batteries are the most vulnerable to corrosion.

Gel cell batteries use a jelly-like mixture of silica and sulfuric acid as the electrolyte. Without a liquid acid, there is no evaporation, which makes them maintenance-free. However, these batteries cannot be charged with fast chargers as exposing them to high amperage situations would damage the jelly and create air pockets.

Absorbed Glass Matte or “AGM” batteries are the latest type which offers many benefits over traditional flooded or gel units, such as longer life-cycle, improved cycling, and vibration resistance. Inside, there are positive and negative paste covered metal plates, divided with a fiberglass matte separator. They are very impact resistant and have the least internal resistance. As with gel cell batteries, these are also maintenance-free.


If you are having trouble starting your car in the morning, the first thing to check should be battery terminals. Corrosion can occur on any car battery, shortening its lifespan and preventing proper operation. However, as you have seen in this article, removing and preventing battery corrosion is a simple job.

If you are having trouble starting your car in the morning, the first thing to check should be battery terminals. Corrosion can occur on any car battery, shortening its lifespan and preventing proper operation. However, as you have seen in this article, removing and preventing battery corrosion is a simple job.



Scroll to Top