Anyone who has spent any time at all around car engines will instantly recognize car battery corrosion. It’s that blue, green, grey crystalline substance that looks like an alien life form in a bad science fiction movie.
It is actually a straightforward chemical reaction. Most 12-volt lead-acid, car batteries (which is to say, basically all car batteries) will have this issue it some point. Corrosion results from the interaction of car metals, battery off-gassing, and the environment.
Corrosion may look scary, but it’s not really dangerous if addressed in a timely manner with proper precautions. In this guide, we walk through everything you need to know about how to clean corrosion from car battery terminals.
What Causes Car Battery Corrosion?
There are actually two types of corrosion to know. They can be distinguished by their color(s).
Batteries have a positive terminal on one side and a negative terminal on the opposite side. The corrosion on the positive terminal is most likely to be blue-green. This results when the following interact and react:
- Copper in the terminal clamp
- Lead in the battery terminal post
- Sulfuric battery acid (seeping through leaks and seams), and
- Electrical current.
The result of the above is copper sulfate. Add in a little moisture from the air, and you get our aforementioned blue-green alien life form.
A white powder-like substance is most often found around the negative terminal. Why? It results from a buildup of lead sulfate crystals. This happens when the battery doesn’t get a full charge. The most common reasons for a less-than-full charge include:
- Repeated short trips (alternator doesn’t have time to fully recharge the battery)
- Faulty alternator
- Too many electrical accessories (e.g., auto infotainment systems, USB ports).
This can happen to even the best car battery. The good news is that corrosion is easily preventable with a little routine maintenance.
What Are the Risks of Car Battery Corrosion?
As we noted earlier, corrosion isn’t the most dangerous thing in the world, but it does need to be addressed. The risks that you need to know fall into two buckets: risks to people and risks to cars.
Risks to People
Remember most of the corrosion on 12-volt lead acid batteries is copper and lead sulfate. Touching it without protection can lead to:
- Skin irritation and mild burning (will also damage clothes)
- Irritation to the lungs if inhaled
- Permanent eye damage.
Also, note that jump starting a battery with corroded terminals can cause sparks. These sparks in rare instances can ignite hydrogen gas in damaged batteries and cause an explosion.
Risks to Cars
Other than that little jump-starting thing noted above, the risks to autos are not all that great. The primary risk is that the battery will not generate enough power to start a vehicle. Murphy’s Law usually dictates that batteries will fail at the absolute worst time.
The acidic nature of the corrosion can also slowly degrade cable connectors. Finally, corrosion can damage car paint. Usually this happens when people get the corrosion on their clothes and then lean on the side of the auto to get underneath the hood.
How to Clean Corrosion from Car Battery Terminals?
To avoid all the risks we just discussed, it is important to inspect your car battery at least once a year and before any long road trips. Make this part of your normal maintenance routine.
Cleaning car battery corrosion is not difficult. For you visual types, this video provides a good overview.
Step 1: Inspect the Battery for Potential Safety Hazards
Many car batteries have a plastic safety cover secured by clips. If that is the case, simply unclip the cover and set it aside. Now that the battery is accessible, the most important things to look for are potential safety hazards. The main culprits are cracked battery cases and leaking battery acid. If you are unsure, consult your local dealer or mechanic before proceeding. If all looks good, you can proceed to cleaning the terminals.
Step 2: Check the Type and Amount of Corrosion
First, always wear the right safety gear. We recommend commercial vinyl gloves or something similar. Most battery terminals will have plastic covers. Usually the “+” is red and the “-” is black. These should be easy to remove. Next, check the battery clamps and cables for corrosion. Remember from our discussion earlier, that the color indicates the type of corrosion. If the cable damage is severe, you may need to buy new cables. Otherwise, you can proceed with cleaning.
Step 3: Disconnect the Battery Clamps
Some people prefer to spoon on a mix of baking soda and water (in roughly equal parts) first to neutralize the acid. This approach will work, but it’s also very messy. Generally, we prefer to wear gloves and remove the clamps first. Use a boxed-end wrench or a socket to loosen the nuts. Once they are sufficiently loose, remove the “-” (negative) clamp first and then the “+” (positive) clamp. Following this sequence with the clamps is very important for safety reasons. Also, avoid touching metal objects (e.g., frame of the vehicle) during this process as it can short out your battery.
Step 4: Create a Baking Soda Solution
As we noted earlier, a baking soda-distilled water combination neutralizes acid. It seems like everyone has a different spin on this, but we prefer to mix 3 tablespoons of baking soda and 3 tablespoons of distilled water. Stir in a bowl until there are no lumps and a consistent paste is achieved. You can modify the ratio slightly if you prefer a thicker paste.
Step 5: Apply the Solution to the Terminals
Use a damp shop rag or old tooth brush to apply the baking soda to the parts of the battery that have corrosion (including the clamps). As can be seen in the above video, the mixture will bubble and foam as it interacts with the corrosion. Let it sit for 5-10 minutes to break down the corrosion before cleaning.
Step 6: Remove the Corrosion
The idea here is to use an abrasive tool to remove the corrosion. Specially made terminal brushes can be purchased for $2 to $3. You can also use wire brushes, or even sandpaper in a pinch. The terminal brushes work well since they are purpose-made for this task. Some people find it easier to use a putty knife (or something similar) to scrape off deposits first and then follow with a terminal cleaning brush or regular steel brush.
Step 7: Rinse the Battery
Used distilled water to rinse away any remaining baking soda mix and corrosion. Either pour it directly onto the battery and clamps or use a handheld spray bottle. Batteries have side vents to release hydrogen gas. Be sure to avoid getting any of the mixture into the vents as that could harm your battery’s performance and shorten the useful life.
Step 8: Wipe Down the Battery
Use a clean cloth to wipe any excess water or debris off the battery terminals and battery case. Be sure the cloth is completely clean with no oily residue. You may have to repeat this step 2 or 3 times to get completely clean. Some people try to use paper towels. That is a mistake. Stick to wash cloths or microfiber cleaning cloths.
Step 9: Prevent Future Corrosion
It would be a shame to go through all this work on your vehicle only to have to repeat the process in a few months. While continuing to wear gloves, apply some anti-corrosion grease or petroleum jelly to the battery terminals. Apply a thin layer around the sides and top of the terminal. This will prevent future corrosion.
Step 10: Reattach the Cables and Protective Casing
Next is basically the reverse of Step 3. This time reattach the “+” battery cable clamp first. Simply put it back on the positive terminal and tighten the bolt to a snug fit (do not over-tighten!). Repeat the process for the “-” terminal. After this is done, put the plastic terminal covers back in place. If your battery has a plastic protector, reinstall that as well.
That’s it! Now you have a clean battery that should reliably start your auto every time you need it.
How to Clean a Car Battery Terminal Without Baking Soda?
Some people just know better and insist on not following standard procedure (yes, I’m one of THOSE people). All joking aside, there are other DIY tips that will work.
Coca Cola is the most common one. In practice, it’s probably messier for your vehicle, but it will get the job done. Buy a 12 ounce can or bottle and pour all the contents on the battery terminals. Be careful not to get any in the side vents. Let it sit for 5 to 10 minutes and remove the corrosion with a brush just like in Step 6 above.
Other DIY cleaning solutions we often see mentioned are vinegar and lemon juice. We recommend that you stick to baking soda and only use a cola if you’re in a pinch. There is no real reason to deviate from what works best.
If you have a car long enough, you will most likely have to deal with a corroded battery at some point. As we noted earlier, corrosion is not a reason to panic but does need to be addressed in a timely manner.
Cleaning car battery corrosion as outlined above is tried and true process. Wear the right safety gear and follow the steps, and you should have no issues. Remember is a cable looks beyond repair, you can always buy a new one.
So, now that you know the process, give your car battery a thorough inspection. An ounce of prevention sure beats being stuck away from home with a car that won’t start!
Tips on vehicle and cable maintenance: https://www.mechanic.com.au/mechanic-advice/car-maintenance-tips/car-batteries/how-to-remove-battery-corrosion
Tips on how to address sulfation: https://batteryuniversity.com/index.php/learn/article/sulfation_and_how_to_prevent_it