How To Replace Battery Terminals in Your Car % Family Handyman

Publish date: 2024-05-19

Introduction

Over my 50 years in the auto repair industry, I've repaired hundreds, if not thousands, of battery cable terminals. But one particularly troublesome situation stands out.

Once while I was charging a battery, the cable clamps became blazing hot. After disconnecting the charger and letting everything cool down, I removed the battery cables, thinking the battery must have internally shorted.

The negative cable, which you always remove first, was fine. However, to my surprise, I found the inside of the positive cable completely corroded and battery post eroded. This kept electricity from flowing into the battery, causing the overheated charger clamps.

I told the customer to replace the battery and the battery terminals, but unfortunately the damage was already done. Due to extreme voltage and amperage surges, the engine control module (ECM) and the electronic air conditioner display/control panel failed within six months.

Corroded battery terminals can cause more problems than just difficulty starting. 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 other sensitive electronics our cars depend on.

What causes corrosion on car batteries?

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.

If the battery terminals in good shape and just dirty, you can clean them yourself. However, if they're damaged, pitted or rotted, or you cannot securely tighten the clamping nuts, it's time to replace them.

Corrosion On Car Battery

How much does it cost to replace car battery terminals?

Depending on where you live, around $130. If you DIY, you'll save a hour's labor charge (according to AAA $47-$215 an hour), the normal 25 percent markup on parts and materials, plus hazardous waste disposal fees.

What safety precautions should I take?

A battery contains sulfuric acid, which can cause serious burns. Always wear gloves and eye protection when working around a battery or jump-starting a car. If you come into direct contact with battery acid, flush with plenty of water and seek medical attention immediately.

How can I identify which car battery terminal is positive or negative?

According to Jon Stull, a National Institute for Auto Safety Excellence (ASE) master technician, look for the positive (+) and negative (-) markings on battery itself. The positive cable should be red or have a red cover. The negative cable should be black or have a black cover.

I find dirty cables confusing to identify. Cleaning the battery should expose the markings. If you're still unsure, use an inexpensive digital volt ohm meter (DVOM) 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 backwards. Either way, you now know how to proceed.

Which battery terminal do you disconnect first, red or black?

Loosening Negative Battery Terminal with Combination Wrench

When to call a pro

Replacing battery terminal ends is a basic DIY project. However, know your skill limits. If you don't feel comfortable working around a battery or don't have the proper tools, call a professional.

Car battery and windshield washer. Close up detail of a Flat-four (boxer) car engine compartment under the open hood

About the expert

Jon Stull spent 19 years as a Ford technician and eight years in the heady equipment repair industry. An ASE master technician for 27 years, Stull is now Pennsylvania Department of Education (PDE) certified automotive technology instructor, preparing the next generation of automotive service professionals.

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