How to Clean Car Battery Corrosion (5 Easy Steps)

Having trouble starting your car? Don’t replace your battery just yet. Older cars often have corroded battery terminals. Corrosion resists the flow of electricity, and can make a good battery act like it needs replacement.

Here’s how to turn a $200 fix into one that’s nearly free.

Identifying Battery Corrosion

corrosion on battery terminal

When your terminals are corroded, you may see a presence of battery acid on or near the terminals. Dried battery acid looks white and crystalline, almost like snow. Sometimes the dried battery acid has a bluish tint to it.

Battery acid corrodes surrounding metals very quickly. If your notice dried battery acid, look for nearby corrosion that appears reddish in color. Reddish corrosion is mostly likely rust. Leaking battery acid is highly acidic and accelerates the corrosion process on surrounding metals.

What Causes Corrosion on Battery Terminals?

Most lead acid batteries are not sealed and leak a small amount of hydrogen and oxygen gas when they are recharged. When this hydrogen and oxygen reacts with other elements, the new compounds may cause corrosion.

Lead acid batteries are filled with an electrolyte that may leak in certain instances. If this electrolyte leaks out of the battery, it can cause corrosion of the battery terminals. If the battery is overcharged, this may increase the chances of the electrolyte overflowing out of the battery.

Sealed Batteries in the Trunk or Cabin

Some vehicle models house the battery in the trunk or cabin. These vehicles require special batteries. These batteries must either be sealed or use special venting systems that dissipate hydrogen gas outside of the vehicle.

If you purchase a traditional lead acid battery and place the battery inside a compartment with no airflow, hydrogen gas may vent inside the vehicle. This could create a dangerous situation, as hydrogen gas is extremely flammable.

Sealed batteries are called valve-regulated lead acid (VRLA) batteries, also known as sealed lead acid (SLA) batteries. An absorbent glass mat (AGM) battery is one type of battery that is constructed for use inside the vehicle.

Sealed batteries are much less likely to corrode, but are often more expensive to replace. If you notice corrosion on a sealed battery, it’s usually best to just replace the battery. This may indicate a leak in the battery, possibly due to a failing seal. You should also clean the battery cables before installing the new battery.

Is Corrosion on a Car Battery Bad?

Battery acid is meant to stay inside the battery. If you notice any battery acid outside the battery, it should be neutralized and cleaned up. Corrosion that results from leaking battery acid can cause all sorts of issues around the vehicle.

These problems range from trouble starting the vehicle to miscellaneous electrical issues, if the ground straps are corroded.

How To Clean Corroded Car Battery Terminals

What You’ll Need

Battery acid is highly corrosive and could cause chemical burns to your eyes or skin. It’s important to wear gloves and eye protection when you clean the battery terminals.

You’ll also want to have some water and baking soda handy. Baking soda is a base (the opposite of an acid). This will help neutralize the battery acid during your cleaning procedure. Grab a rag, some shop towels, or paper towels to wipe off and dry the cleaning solution.

Purchasing a battery terminal cleaner will greatly speed up the cleaning process. This product is very inexpensive and can be found for less than $10. A wire brush or even some sandpaper should do the job as well.

You may want to grab a can of battery terminal protector to prevent future corrosion. Some people use dielectric grease or petroleum jelly instead, but battery terminal protector is made for this specific purpose.

1) Disconnect and Remove the Battery

old battery

Starting with the ground terminal (usually the negative terminal), disconnect both leads from the battery. The battery cables usually use a socket size ranging from 8 mm to 13 mm, but will vary depending on the vehicle.

Remove the battery to give yourself a bit more room. This will also make it easier to spot and clean and residual corrosion that leaked down from the battery.

Be careful when lifting the battery; many batteries weigh close to 40 lbs, and are placed in an awkward place in the engine bay that makes lifting them difficult. Grab a friend to help you out if you need a hand.

2) Rinse the Terminals

Using a solution of baking soda and water, rinse the terminals to remove as much of the corrosion as you can. Some of the acid will come off in this step, but you will probably have to use a tool to scrape the rest off.

3) Scrub the Terminals

Using your wire brush or battery terminal cleaner, scrape the metal terminals and battery cables until both surfaces are shiny. The battery terminal cleaner will scuff the metal so the battery cables will have good contact with the battery posts.

4) Dry the Terminals

Once you’ve removed all the corrosion, dry the surfaces using a rag, paper towel, or shop towel. Make sure there’s no residual moisture on the posts or cables.

5) Reinstall the Battery

Reinstall and reconnect the battery. Connect the positive cable first, then the negative cable. If you’ve opted to apply a battery terminal protector, only apply this once the battery cables are reinstalled.

Lead Acid Battery Maintenance


Since traditional lead acid batteries are not sealed, they actually require a bit of maintenance. Beneath the caps on top of your battery is the electrolyte solution. As the battery ages, the water in this solution may evaporate. This happens as hydrogen and oxygen vent from the battery.

If you pop the caps and notice the water level is low, add distilled water until the water level is full. The “full level” approximately a half inch below the fill well. Check the bottom of the battery cap to make sure your new water level allows the cap to be reinstalled without forcing any of the electrolyte out of the top of the battery.

Make sure you only top off the battery when it’s fully charged. It’s also important to wear gloves and eye protection when performing battery maintenance. These simple steps are a great way to maintain your battery yourself, saving you the cost of a replacement.


2 thoughts on “How to Clean Car Battery Corrosion (5 Easy Steps)”

  1. Good article.
    In the first line of “Cleaning Corrosion Off a Car Battery”, I think what you meant to say is “the first step is to disconnect the cables from the battery terminals”.


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