How to clean battery corrosion on car terminals and in devices

Step by step: how to clean battery corrosion on car terminals and in devices

Safety first. Wear gloves and safety glasses: car batteries contain sulfuric acid and leaking alkaline batteries contain a caustic electrolyte. If any gets in your eyes, flush with running water for at least 15 minutes and get medical help. Take off rings and watches, never let a metal tool touch both terminals at once, and keep sparks and flames away from a car battery. Replace a battery that is cracked, bulging or leaking from the case.

1. 1

   Work out which kind of corrosion it is

   Crust on a car battery’s posts and clamps is from the battery acid and charging gases, and baking soda neutralizes it. White crystals or fuzz inside a remote, flashlight or toy come from a leaking alkaline battery, which is caustic, so a mild acid like vinegar or lemon juice neutralizes it. Put on gloves and glasses either way.

2. 2

   Disconnect the car battery, negative first

   Turn the car off and remove the key. Loosen the black (negative) clamp and lift it off first, then the red (positive) one, tucking each cable away so it cannot touch the post. For devices, simply remove all the batteries and throw out any that leaked.

3. 3

   Car: brush on baking soda and water

   Stir about 1 tablespoon of baking soda into 1 cup of water and brush it onto the posts and clamps with an old toothbrush. It will fizz as it neutralizes the acid. Add more until the fizzing stops.

4. 4

   Car: scrub the posts and clamps clean

   Scrub the battery posts with a terminal brush or wire brush until they are bright gray lead, then clean the inside of each clamp with the other end of the brush. Corrosion on the clamp’s inner surface is what causes slow cranking, so do not skip it.

5. 5

   Devices: dab the contacts with diluted vinegar

   For the battery terminals in toys, remotes and flashlights, mix equal parts white vinegar (or lemon juice) and water. Dip a cotton swab or toothbrush and dab the springs and contacts until the white crust dissolves, using a dry swab to lift it out. Use as little liquid as possible near circuit boards.

6. 6

   Rinse lightly and dry completely

   Wipe car terminals with a rag dampened in clean water to remove the baking soda, then dry them with a clean rag. In a device, wipe the contacts with a swab barely dampened in water, then let it air-dry for at least an hour. Bright, shiny metal means the contact is clean; lightly sand dull spots with an emery board.

7. 7

   Protect the terminals

   Coat car battery posts and clamps with a thin layer of dielectric grease or spray them with a terminal protector to slow new corrosion. Felt anti-corrosion washers under the clamps also help. Device contacts do not need grease.

8. 8

   Reconnect positive first and test

   Attach the red (positive) clamp first and tighten it until it will not twist by hand, then the black (negative). Start the car and check that the clamps stay tight. For devices, put in fresh batteries of the same brand and type, and recycle the leaked ones.

Car battery corrosion versus a leaking AA battery

They look similar but need opposite neutralizers: baking soda for car battery acid, and a mild acid for alkaline leakage. Duracell’s FAQ says to clean alkaline leakage from device contacts with a toothbrush or cotton swab dipped in a 50/50 mix of vinegar or lemon juice and water, in a ventilated area, wearing gloves and glasses.

What the color of battery corrosion means

The color tells you which metal is corroding. According to Interstate Batteries, white crust is corroded lead, zinc or aluminum; blue or green is copper in the wiring or clamps; and brown or red is iron or steel.

Interstate names hydrogen gas from the battery as the most common cause, along with an alternator that overcharges the battery and acid leaking from a cracked case. Heavy corrosion that returns within weeks is a sign to have the battery and charging system tested. Interstate also advises against cleaning terminals with cola, which can cause new problems.

Why you disconnect the negative terminal first

Taking the negative cable off first means a wrench that slips onto the car body cannot create a short circuit. Interstate’s disconnect guide says to remove the black negative clamp first, then the red positive, and to reverse the order when reconnecting: positive on first, then negative.

It also recommends removing jewelry, wearing gloves and glasses, and never letting a wrench touch the other terminal. If you are not comfortable working on the battery, any auto parts store or repair shop can clean and test it.

How to prevent battery corrosion and leaks

Most household leaks come from batteries left in devices too long, and most car terminal corrosion builds slowly where it is not protected.

• Take batteries out of devices you will not use for a while. Energizer’s battery care tips also say not to mix old and new batteries or different types, and not to store them somewhere hot.
• Replace all the batteries in a device at the same time with the same brand and type.
• Coat clean car terminals with dielectric grease or protector spray, and check them at every oil change.
• Keep the top of a car battery clean and dry, and make sure the hold-down clamp stops it from moving.
• Recycle or drop off used batteries rather than tossing them in a drawer. The EPA’s used battery guide explains which types to recycle and where.

Grimy electronics around the house need a gentler touch; see how to clean a keyboard.

Mistakes to avoid

• Removing the positive cable first, or letting a wrench bridge both posts.
• Using baking soda on alkaline battery leaks, or vinegar on car battery acid.
• Pouring water over a device to rinse it, instead of using a barely damp swab.
• Cleaning only the posts and leaving corrosion inside the cable clamps.
• Putting new batteries into a device before the contacts are completely dry.
• Reinstalling the old leaked batteries instead of recycling them.