Car Battery Corrosion: How to Clean a Corroded Car Battery

Open the hood on most vehicles that have had the same battery in them for some time and you’re bound to see at least some corrosion forming on the tops of one of the two posts of the battery. When you’re faced with purchasing a new battery, you may be asked about different forms of protection for the terminals. To some, this may seem like crazy “snake oil” or an unnecessary item, but it’s not. To understand its function as a protector against corrosion, it’s important to understand exactly what’s happening to cause it.

What Causes Car Battery Corrosion?

Battery corrosion around the posts of the battery is caused by the sulfuric acid and hydrogen gas vapor that can escape from the battery. Sometimes this vapor is vented out of the top vent blocks on the battery, but other times, small amounts of this vapor leak out in the area between the posts and where they seal to the plastic battery casing. This vapor mixes with other gas under the hood, the heat of the engine, the differences in lead composition between the posts and the terminals, the copper of the battery wires, and creates corrosion. Under the hood of a car, temperatures can exceed 250 degrees, and this heat causes the metal of the posts and the plastic of the casing of the battery to expand at different rates. This is the reason why you rarely see corrosion on the posts of a battery that’s under a seat, or in the trunk of a car. These batteries aren’t exposed to the extreme temperatures you find under the hood.

Cleaning corrosion off of your car battery terminals is not a complicated process. You don’t have to take the car to a mechanic or rely on any advanced, complicated techniques to get your battery looking like new. You can either use one of our battery cleaning solutions or a combination of baking soda and water. It’s recommended that you use either a battery cleaner brush tool, or a very small wire brush to do the cleaning, along with a solution.



First, check the area around the battery for any leaking acid. If you have a battery that is leaking acid and is wet in the tray or around the bolts, this is potentially a sign of a bigger issue and not just regular battery corrosion. The battery should be removed, inspected, and tested, and the battery tray/area should be cleaned with baking soda and degreaser.

With a mix of some baking soda and water, you can usually neutralize and remove all the corrosion on the terminals. To do this, start by assembling the essential tools and products for the job. You’ll want some protective gloves for safety reasons. Next, grab a box of baking soda from your kitchen pantry along with some water. Your battery brush, wire brush, or even an old stiff-bristled toothbrush will be a handy tool to scrub the terminals. You should also get some old rags so you don’t mind getting dirty.

Remember, if you unhook the battery terminals, your cars electronics will lose their memory power, and some vehicles need a battery tender hooked up at all times to keep 12V of power to the engine’s computer. Check to make sure your car isn’t one of these, and if not, unhook the battery terminals by loosening the bolts on the clamps so that the posts and the terminals can be properly cleaned. When loosening heavily corroded terminals – if you encounter ANY resistance and the bolt is too tight – stop. Mix up some solution, and don’t risk breaking the terminal.


The baking soda and water should be enough to do the job efficiently. Start with 1 tablespoon of baking soda to 1 cup of water and mix it thoroughly until all the baking soda is blended in. If there’s heavy corrosion on battery terminals, it may be better to use a specialized battery terminal cleaner. These are often aerosolized for easy application.


Scrub all the corrosion off the terminal and spray the terminal’s bolt with a little penetrating oil like WD40. Next, attempt to loosen the bolt and remove the terminal for further cleaning.

Many times, the terminal is corroded so badly that it must be replaced completely. If so, AutoZone sells replacement terminals and terminal end kits. Once you clean your terminals and/or replace them, clean the battery posts and the top of the battery, rinse thoroughly with clean water, then dry them off with a rag. From here, let’s talk about protecting those terminals during future use.

How to Protect Your Car Battery from Corrosion

One of the easiest and best solutions to help protect against corrosion is by using felt battery washers and a protective grease. Battery washers are chemically treated to help absorb that vapor at the source right at the base of the post before it gets to the terminal. Battery grease is a silicone-based grease. Unlike petroleum jelly which is, like its name says, petroleum based, silicone grease will last longer when exposed to under-hood heat. Coat the top of the washer and the terminal in protective grease before installation, and that’s it. Over a long period of time, these washers lose their ability to absorb that vapor. They don’t last forever, but they help keep the terminals clean for several years. It’s usually long enough to get you through to your next battery replacement.

On a side post battery, the post is actually BELOW the acid level, so a felt washer, even though it could be used, is not going to provide the level of protection as it does on a top post battery. This is where buying terminal grease will help protect. When a side post battery is subjected to heat and has the same separation between the battery and the post, it can actually leak acid. This corrodes the terminal, sometimes so badly that the bolt seizes in the bolt hole. By applying terminal protectant into the bolt hole and on the terminal, you are creating a barrier that works like an anti-seize.

Battery terminal grease also provides great protection for non-automotive batteries. Marine applications, ATV, lawn and other small engines that operate on a battery are subjected many times to extreme heat. These batteries don’t offer the ability to use a washer on them, but do allow you to coat the terminal lugs, or bolts, with protectant.

When it comes to your vehicle, few things are more frustrating than dealing with battery trouble. If you follow these steps of how to clean car battery corrosion, you are much less likely to experience these issues by taking care of corrosion when it appears.

If you need Trustworthy Advice or clarification on how to clean car battery corrosion or you’re trying to figure out the right product to work for your needs, AutoZone associates are there to help.

If the job is too big for you, seek out one of our Preferred Shops to help you do the job.

Advice, how-to guides, and car care information featured on and AutoZone Advice & How-To’s are presented as helpful resources for general maintenance and automotive repairs from a general perspective only and should be used at your own risk. Information is accurate and true to the best of AutoZone’s knowledge, however, there may be omissions, errors or mistakes.

Be sure to consult your owner’s manual, a repair guide, an AutoZoner at a store near you, or a licensed, professional mechanic for vehicle-specific repair information. Refer to the service manual for specific diagnostic, repair and tool information for your particular vehicle. Always chock your wheels prior to lifting a vehicle. Always disconnect the negative battery cable before servicing an electrical application on the vehicle to protect its electrical circuits in the event that a wire is accidentally pierced or grounded. Use caution when working with automotive batteries. Sulfuric acid is caustic and can burn clothing and skin or cause blindness. Always wear gloves and safety glasses and other personal protection equipment, and work in a well-ventilated area. Should electrolyte get on your body or clothing, neutralize it immediately with a solution of baking soda and water. Do not wear ties or loose clothing when working on your vehicle.

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