Why Do Car Batteries Corrode

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If you’ve been driving for a while and ever popped open the hood, there’s a chance you’ve seen a white, powdery substance collecting on top of your battery. This substance is the result of battery corrosion. It’s a very common condition that is easily fixed, but if left unchecked can cause real problems later on. 

Car batteries are basically large boxes filled with a mixture of sulfuric acid and water. This solution comes into contact with lead alloy plates, causing an electrical charge. Car batteries usually corrode because one or more substances – the sulfuric acid, or its resulting gases – is leaking out of the battery and coming into contact with your battery terminals. When that happens, the resulting chemical reaction creates that powdery material. 

This substance (which is scientifically known as a sulfate) can eventually start to interfere with the battery and its proper use, eventually cutting the battery off from the terminals altogether. When this happens, the car won’t sart any more. This is why it’s important to know how to clean this corrosion, should you start to notice it.

Optima Batteries 8020-164 35 RedTop Starting Battery

What Causes Battery Corrosion?

Even though a corrosive battery looks disgusting, it’s actually a very common issue that can happen due to a number of reasons. 

One reason is that the battery might be leaking fluid. This is especially true of older batteries that allowed a user to top it off with water. Battery fluid would escape through tiny exhaust vents, come into contact with terminals, and begin to corrode. 

Even if a battery does not allow users to add water, the battery still has tiny vents to allow for a small amount of sulfuric acid to escape from the battery from time to time. Just like the fluid itself, when this gas touches the battery terminals it can begin to cause that corrosive buildup. 

Third, batteries that are tool old can also just naturally start to corrode. Most batteries only have a useful life of somewhere between five to seven years. After that span of time, they begin to degrade, losing their ability to work properly. At the same time, more and more gases or fluids from inside the battery can escape, leading to more corrosion.

Also Read: Car Battery Leaking From Top

Step by Step Guide in Removing Car Batteries Corrode

The good news about all of this is that removing this corrosion is actually extremely easy. It takes almost no tools or technical know-how. Here’s how you do it.

1. Remove The Battery Cables.

This is actually the most technical step of the whole process, and requires a small adjustable wrench. Loosen the nut on the side of the battery cable. Soon, the cable will loosen up. Once that happens, you should be able to slide it off the terminal. 

2. Look for Corrosion On The Inside

Once the cables are removed, inspect them. Sometimes the corrosion will have made it to the cable, sometimes not. If not, then you’re good. If so, then you will need to clean them as part of the next step.

3. Clean the Battery Terminals

Cleaning the battery terminals (and possibly the cable) involved taking a small, stainless-steel wire brush and basically scouring the terminals to get the sulfate off. It might scuff up the terminal a little, but don’t worry: you’re not damaging the battery at all! Scrub the terminals until the corrosion has been removed. In stronger cases, you can add a dab of toothpaste, believe it or not, to help. If you don’t want to scrub, you can also spray a battery terminal cleaning agent.

4. Wipe Down the Terminal

Once finished, wipe down the terminals with a dry cloth to remove the last of the corrosion. Then, install battery terminal protectors – this sounds fancy, but they are nothing more than small felt disks that go over the terminals and help prevent corrosion from building up. 

5. Put The Battery Cable Back on the Terminals

Once you have finished, put the battery cable back on the terminals – make sure you place them back on the correct ones! – and slide them all the way down so the terminal is completely covered. Take the wrench and tighten it back up. 

6. Add a Battery Corrosion Preventative

Finally, add a battery corrosion preventative. There are dedicated sprays you can find at your local auto parts store. You can also spray the terminals with WD40 or add a tiny layer of petroleum jelly. In all cases, the preventative acts as a barrier, protecting the terminals from the corrosive elements that can come into contact with them.

Also Read: Car Battery Voltage Too High


As you can see, cleaning your battery terminals is not a difficult task. The entire process from start to finish might take you ten to fifteen minutes, no more. And yet, it is so important to ensuring a long life for your car battery. If you want to help keep your car running for years to come, simple maintenance procedures like this are crucial.

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