Cleaning your car battery and corroded battery terminals is an important part of keeping your vehicle starting and running smoothly.
Time 15 – 20 Minutes
ComplexityBeginner
Cost$10 - 25
Introduction
Cleaning your car battery and corroded battery terminals is an important part of keeping your vehicle starting and running smoothly.
If your car cranks over slowly, headlights or other lights are flickering, or the battery terminals are covered in a whitish, bluish or greenish residue, it’s time to clean battery corrosion from the battery cable terminals. Over my 50 years in the auto repair industry, I’ve cleaned battery corrosion from the terminals of hundreds, if not thousands, of vehicles.
Once, when charging a battery, the charger clamps became blazing hot. After letting everything cool down, I removed the battery cables. The negative cable, which you always remove first, was fine. However, to my surprise, I found the inside of the positive cable completely corroded. This kept electricity from flowing into the battery, causing the clamps to overheat.
Although the corrosion buildup you see on a battery terminal is bad, the corrosion you don’t see can be even worse. Even minor corrosion between the inside of the battery terminal and the battery post can reduce alternator output and lower available voltage to the starter motor. That can stress your starter motor and charging system and cause early failures of electronic devices and components our cars depend on to keep running.
What Causes Battery Corrosion?
Hydrogen gas from sulfuric acid released from a lead-acid battery mixing with moisture and road salts causes a chemical reaction that corrodes battery terminals. Here’s how to neutralize battery acid.
If the battery terminals are in good shape and just dirty, you can clean them yourself. However, if they are damaged, pitted or rotted, or you cannot securely tighten the clamping nuts, here’s how to replace them.
How To Prevent Battery Corrosion
In addition to the specific steps listed below to prevent battery corrosion, here are other tips to help keep your battery terminals corrosion-free:
- Inspect your battery for leaks, cracks or damage, and clean cables and terminals as part of your regular preventive maintenance schedule.
- Install battery terminal covers and ensure the battery is securely held in place to keep it from bouncing around and shorting against grounded car parts.
- Use a battery trickle charger or maintainer to help your battery stay fully charged.
Ahead, you’ll find advice from experienced Automotive Service Excellence (ASE) and manufacturer-certified technicians who will guide you through the steps to clean battery corrosion and help extend the life of your battery.
Tools Required
- Battery cable puller (optional)
- Battery memory saver with a fresh 9 volt battery or a battery jump starter
- Battery terminal cleaning tool or sandpaper
- Old toothbrush or stiff non-metallic parts cleaning brush
- Safety glasses
- Slip joint pliers (optional)
- Socket/ratchet set
- Work gloves
- Wrench set
Materials Required
- Baking soda or spray battery cleaner
- Battery terminal anti-corrosion washers
- Battery terminal covers (if missing)
- Battery terminal protective spray or grease
- Bucket of clean water or garden hose
- Dielectric grease or Vaseline
- Disposable container
- Disposal shop or paper towels
- Distiller water (optional)
Watch Car Battery Corroded? Here’s How To Clean It
Project step-by-step (10)
Step 1
Take safety measures
A battery contains sulfuric acid that can cause serious burns. Always wear gloves and eye protection when working around a battery. Smoking, flames, sparks, or other ignition sources can cause a battery to catch fire or explode. Exercise caution when jump-starting or working near a battery with metal tools to prevent short circuits and sparks. If you come into direct contact with battery acid, flush with plenty of water and seek medical attention immediately.
Step 2
Connect battery memory saver backup
Don’t skip this step. A battery memory saver supplies current to different computers to avoid deleting, radio, keyless entry and clock memory settings. It will also save other critical data, including engine monitor status, that if not preserved, will turn on the check engine light and cause drivability issues.
Here’s how to do it:
- Plug a battery memory saver, a battery jump starter or an OBD II memory saver into your vehicle’s 12 volt power receptacle.
Step 3
Cleaning the battery
- Mix one tablespoon of baking soda with two cups of hot water in an old, clean plastic cup.
- Remove heavy corrosion from the outside of the terminals with the plastic parts cleaning brush.
- Clean the battery case with an old toothbrush or parts brush and baking soda solution or spray battery cleaner.
- Flush the battery with clean water and wipe dry. Be careful — do not splash the water or cleaning solution on you or other parts of your car.
- Dry the battery with clean, disposable shop rags.
Step 4
Disconnect the battery terminal clamps
According to ASE master technician Jon Stull, look for the positive (+) and negative (-) markings on the battery itself. The positive cable should be red or have a red cover. The negative cable should be black or have a black cover. First, determine the positive and negative terminals.
- Always disconnect the negative (-) black battery terminal first.
- Always reconnect the negative (-) black cable last.
- Remove battery terminal protective covers.
- Loosen the negative (-) terminal clamping bolts with a wrench or socket.
- Disconnect the terminal clamp from the negative (-) battery post.
- Do not twist the terminal clamp if it’s stuck or “frozen” to the battery post. Use a battery terminal puller to carefully remove the terminal.
- Repeat for the positive (+) post.
Even after a lifetime in the automotive repair industry, sometimes I find identifying dirty or corroded battery cables confusing. Cleaning the battery should expose the (+) and (-) markings. If you’re still unsure, use an inexpensive digital volt ohm meter (DVOM) to determine which is which. If you connect the positive lead of the DVOM to the positive battery terminal, and the negative lead to the negative battery terminal, the DVOM should display the battery voltage, around 12.6V. If the DVOM displays a negative (-) symbol in front of the battery voltage reading, you’ve connected it backward. Either way, now know how to proceed!
Step 5
Cleaning the terminals
- Deep clean the battery posts and terminals with a battery terminal cleaning tool (recommended) or, in a pinch, 120-grit sandpaper.
- Use caution and remove only enough material to fully clean battery corrosion from the posts and terminals. Removing too much material from the posts or terminals will cause poor connections and additional repairs.
- Clean any dirt from the posts with a damp paper towel.
- Dry the posts with clean, disposable shop rags.
Step 6
Install anti-corrosion washers and apply grease
- Install new battery terminal anti-corrosion washers onto the battery posts.
- Coat both terminals and battery posts with dielectric grease (preferred) or Vaseline.
- This step helps to lubricate both the terminals and posts, protecting them from future corrosion.
Step 7
Reinstall terminal clamps
Always connect the positive/red terminal first.
- Push down the terminal clamps onto the post until they touch the anti-corrosion washers or top of the battery. In most applications, the top of the post will stick up slightly past the top of the terminal end.
- Securely fasten terminal clamp nuts with a wrench or socket.
Step 8
Corrosion prevention
- Before sliding the battery terminal covers back onto the terminal clamps, coat both terminals with battery terminal protection grease (preferred) or Vaseline to prevent corrosion.
- Using protection grease or Vaseline gives you more peace of mind and double the protection.
- Fortunately, now that you know how to clean corroded battery terminals, you can do this repair without too much trouble. Plus, extra protection is never a bad thing.
Step 9
Final steps
ASE master technician John Alcaro advises checking the battery fluid level if your car has a non-maintenance-free battery. “Top [the battery] off with distilled water if the [fluid] level is low,” says Alcaro.
Step 10
FAQ
What will happen if I don’t clean battery corrosion?
Unfortunately, over my career, I have seen the damage caused by not cleaning corroded battery terminals —and it’s more serious and costly than just difficulty starting. Extreme voltage, and amperage surges from potential arcing between a corroded terminal clamp and battery post can quickly cause an engine control module (ECM), the electronic air conditioner display/control panel or any of the other sensitive, and expensive electronics in our cars and trucks to fail.
About The Experts
- Jon Stull is an ASE and Ford certified master technician, PennDoT certified emissions and safety inspection instructor and inspector and a Pennsylvania Department of Education (PDE) certified Career and Technical Education automotive technology instructor at North Montco Technical Career Center in Lansdale PA.
- John Alcaro is a former repair automotive shop owner and has been an ASE master technician for over 35 years. He is a PennDoT certified emissions and safety inspection instructor and inspector, and PDE certified automotive technology instructor at North Montco Technical Career Center.
Sources
- Duffy, J. (2022). Modern Automotive Technology (10th ed., pp. 359, 368-37). The Goodheart-Willcox Company, Inc., Tinley Park, IL.
- John Stella, ASE technician, Faulkner Collision (Interview, Jan 15, 2025)
