What Causes Car Battery Corrosion On Positive Terminal: How to Clean & Prevent

Hi, I'm Luis Johnson, an automobile technician, and power equipment professional. By profession, I'm a businessman and operate a car workshop. I have created this...Read more

Developing corrosion on the positive terminal of a car battery is a common thing and not a dangerous thing to worry about. However, if the corrosion goes out of control, that can put a ton of risks to the rest of the parts of your car, including the engine.

The reason for a car battery to develop corrosion on the positive terminal is overcharging the battery. Driving the car for a long without using the electronics like GPS, DVD, radio, speakers, lights, etc., can cause corrosion.

Well, that might sound odd as you’re corroding the terminal by not consuming energy! This has a lot more technicalities in it though. And will make a lot of sense as we discuss this through.

So, let’s talk about what causes car battery corrosion on the positive terminal, how to clean it, and prevent it.

Know How The Corrosion Develops

As stated, overcharging is the primary reason why the battery terminal develops corrosion. Before we jump into the sweet part, you need to know how the battery charges and discharges. Here’s what you need to know:

How The Battery Charges

As corrosion is a negative outcome of overcharging, you need to know how the charging process takes place.

How The Battery Charges

The primary job of the car battery is to start the starter motor. That helps the combustion engine to reach the minimum RPM threshold to start the engine.

Once the engine is started, there’s another part of the setup called an alternator that recharges the battery.

How The Battery Discharges

Recharging the battery starts from the alternator and ends up in the negative terminal with the positive terminal in between. The positive terminal works as the mediator to take all the load in the beginning.

How The Battery Discharges

The negative terminal is the one that discharges the battery by powering the electronics in the battery. As you use the radio, GPS, headlight, etc., they draw power from the battery through the negative terminal.

The battery maintains a balance between discharging and recharging on the go charging and discharging. If it continues to balance well, corrosion won’t take place, and topping up battery water will keep you going just fine.

What Causes Car Battery Corrosion On Positive Terminal?

The battery in your car has two terminals, the positive being the culprit you’re dealing with. Well, the main reason why the positive terminal of your car battery has developed corrosion is overcharging.

What Causes Car Battery Corrosion On Positive Terminal

But that doesn’t happen in one day or a week. It, in fact, sometimes takes months to develop corrosion to a level when you can’t ignore cleaning it. Here’s everything you need to know about it; from the cause, to how the corrosion develops:

Overcharging the battery

When you’re not consuming the electricity produced by the alternator through the negative terminal, you’re providing the battery with a one-way flow of current. That puts pressure on the positive terminal as the alternator keeps trying to recharge the battery.

As the positive terminal takes in more and more current without discharging, it takes more stress and develops corrosion. If the negative terminal also had the same amount of stress by discharging, there would be a balance between the two.

The technical aspect of this process goes even further, as it goes:

Hydrogen And Electrolyte leakage

The positive terminal develops corrosion when you’re charging the battery more than you’re discharging, thus emitting hydrogen gas from the sulfuric acid inside the battery.

That gas reacts with the ambient air around the battery. This accelerates if you have salty air around your car or moisture elements in the engine bay.

Over Filled Electrolyte

You refill the battery every once in a while with distilled water which you do when you see low water symptoms. If you make the mistake of overfilling the water, the battery tends to leak the electrolyte as the car shakes.

To prevent this from happening, you must top the battery off with water just to the right point which we talked about in our previous article.

Bad Clamps And Battery Age

As the battery ages, the clamps tend to degrade over time as a natural process. That way, the ability of them to conduct electricity also follows downwards.

Besides, the refiling hole caps also start to loosen a little bit, which, as you can imagine, plays a role in higher hydrogen leakage. As an obvious outcome, the car battery tends to develop more corrosion.

A Bad Alternator

If your car has a bad alternator, which is the sole part of the engine that charges the battery, you can end up with excessive corrosion! Oftentimes, the bad alternator cannot supply a steady stream of electricity at a proper scale.

When this happens and the battery cannot draw a constant flow of current, the positive terminal gets hit and becomes unstable. Corrosion comes into play as the byproduct of this frequent electrical surge.

So, be sure to check the alternator when you do an inspection.

Negative Terminal Also Can Develop Corrosion

Now, understanding the process, you can tell, that the negative terminal also can corrode. Just like the positive terminal develops corrosion for overcharging, the negative terminal also can develop corrosion if you undercharge the battery.

If the electronics in your car consume more electricity than the alternator or the battery can produce, you’re falling short of electricity. That’s when you’re putting stress on the negative terminal and much more likely to develop corrosion on it.

Corrosion on The Battery Terminal: Aftermath and Cleaning

So, you have corrosion build-up on the positive terminal of your car battery, what happens now? Can it make an issue? If yes, how to clean it properly? Let’s talk about the aftermath then!

Corrosion Is Bad: Safety Precautions

First off, if you can see the corrosion has worked its way deep into the connecting wire, this is a bad sign, especially if it’s a modern high-end car. This might indicate that the corrosion has also made its way into the engine, even to the alternator.

In such case, if you’re not a professional in it, you better make an appointment with a mechanic.

Secondly, the corrosion is made of sulfuric acid and hydrogen gas! Definitely not the safest thing to get your hands on! Touching the corrosion with a bare hand may cause skin issues and contacting your cloth to it will damage the cloth over time.

So, be sure to put on plastic gloves before you start working. Putting on appropriate clothing is also a great idea.

Thirdly, Although the corrosion is sitting on the terminal area when you wiggle the dusty powers around, they can get airborne. If it does, this can be a big issue for your eyes as they’re close to the corrosion.

So, make sure you have your safety goggles on before you start working with the corrosion, rust, or other things in the engine bay.

How To Clean The Corroded Car Battery Terminal?

Once you have your safety goggles and gloves on, get these things for the cleaning process:

  • A torque wrench with an extender
  • Clean microfiber rag or towel
  • Baking soda
  • Battery Terminal cleaner spray (To clean the corrosion)
  • Terminal scraper or sandpaper (To clean the post and harness)
  • An anti-corrosive spray

Got the cleaning tools in hand? Now let’s go through the cleaning process:

How To Clean The Corroded Car Battery Terminal

Take The Battery Off The Bay

Some people do the cleaning while the battery is still attached to the car. However, taking it off is safer, especially if it has a lot of corrosion to deal with.

First, use a torque wrench and undo the bolt(s) that is holding the battery in place. Then undo the screws that hold the wire harness to the battery posts.

Here, you must unscrew the negative (black wire) terminal first, then the positive (red wire) terminal. Now you can take the battery off the bay.

Dry Clean Everything

Put the battery inside a large bowl or plastic sheet where disposed rust and corrosion can sit without contaminating the work area.

If the corrosion is hard, pry them off, then take a soft brush to dry clean them as much as possible.

Clean With Terminal Cleaner

The best option to clean a corroded battery terminal is by using a battery terminal cleaner. It’s ready to go without prep, easy to use, and easy to clean afterward. However, it’s obviously more expensive than using just baking soda.

Dry Clean Everything

Simply spray over the corroded areas, let the spray sit and do its job, wait for a minute or so, and wipe things off. If you have deeper corrosion, you can do another pass for deeper cleaning.

Do this for all the parts including the battery top surface, the terminal posts, and of course, the wire harnesses. Both the negative and positive, separately.

Clean With Baking Soda

If getting a terminal cleaner isn’t an option right now, using baking soda to clean the battery terminal is just fine.

Take a plastic cup, fill it with water, pour baking soda in it, mix well, and you’re ready with your cleaning solution.

Dip a piece of cloth into the solution, wipe the battery posts and grooves with it, and make sure the solution reaches every inch of the corrosion.

Use a fair amount of liquid, but be sure it’s not enough to dip into the cap vent. That will ruin the battery and might render it dead.

As for the wires and harnesses, dip the head into the solution, including the contact point like this:

Cleaning car battery positive terminal With Baking Soda

Once cleaned, use another piece of clean cloth to wipe everything down, and you should have a nice and tidy battery.

Clean The Post And Harness

You now have a battery cleaned from corrosion, but the cleaning isn’t complete yet. Before you can assemble things, you need to clean the post and harnesses from rust.

Take a terminal cleaning scraper tool and clean the wire harness terminals as well as the battery posts. A piece of sandpaper will do the job just fine if you don’t have a dedicated tool. Just roll the paper, and clean the contacts inside and the post.

Put Everything Together

The cleaning process is over. You can now put everything together and go driving. Simply reverse the process by putting the battery in place, contacting the Positive terminal first, then the negative one.

And don’t forget to clean the battery holder tray before putting the battery in place. This tray also can cause issues if any corrosion remains untouched there.

You can now secure the battery in place using the holding plate. Use a torque wrench instead of an adjustable one, and don’t put too much pressure securing it.

Seal With Anti-Corrosive Spray

Before you close the engine bay, don’t forget to apply an anti-corrosive spray on the terminals where the corrosion might develop over time.

You can also apply a coat of Vaseline directly to the post before screwing the terminals on them. It will keep the post from developing rust too quickly.

Final Words

Now that you know what causes car battery corrosion on the positive and negative terminals, you should have a course of action now.

Just to point you out,

Here’s why the terminals corrode:

  • If you drive for long and use fewer electronics, the positive terminal will corrode
  • The age of the battery has to do with it too: too old are more prone to corrode
  • If you drive short distances and use electronics often, the negative terminal corrodes
  • If you overfill water into the battery, the electrolyte inside can spill and corrode

What to do to prevent and clean:

  • Don’t overfill the battery with water while you’re doing so. Know the deadline
  • Use good copper clamps and connect them well to the battery posts
  • Make sure the seal caps are properly sealed to prevent electrolyte leakage
  • Use baking soda or terminal corrosion cleaner spray to clean them periodically
  • Use petroleum on the posts and apply an anti-corrosive spray while assembling

Hi, I'm Luis Johnson, an automobile technician, and power equipment professional. By profession, I'm a businessman and operate a car workshop. I have created this site Batteryquery to help people purchase the right battery for their vehicles. The reason behind creating this site is to help my customers purchase the right car battery who often purchase the wrong one due to their lack of knowledge.

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