Rick's Free Auto Repair Advice

Battery terminal corrosion

Battery terminal corrosion causes

When your car battery terminals corrode, they develop a white or blue powdery substance. The white powder is lead sulfate and the bluish powder is copper sulfate. You’ll see copper sulfate formation most often if the battery terminal material contains copper.

Battery terminal corrosion is caused by leaking sulfuric acid and sulfuric acid fumes

Any time liquid battery acid or heated sulfuric acid fumes escape from the battery, it can cause corrosion at the battery posts and terminals. As the battery case expands and contracts, battery acid can leak through the gap between the case and the battery posts. Sulfuric acid fumes can also escape from the battery vents when the battery is hot or overcharging.

How the battery corrosion happens

When your battery sits in a discharged state, white powder forms on the negative battery terminal

The white powder is caused by lead sulfate. Sulfate crystals form on the lead plates in the battery. When the battery sits in a discharge state long enough, the lead sulfate starts to cover the top of the plates and eventually creeps up to the battery post through a gap between the case and the post.

The white power on car battery terminals is lead sulfate

It forms when you combine lead, sulfuric acid and water: Lead (Pb) + Sulfuric Acid (H2SO4) + Water (H2O) = Lead Sulfate (PbSO4). If your battery terminals are made with aluminum, the powdery substance can also contain aluminum sulfate.

Blue powder on car battery terminals is copper sulfate

It’s formed when you combine copper, sulfuric acid, and water with electrical flow

Copper (Cu)+ sulfuric acid (H2SO4) + Water (H2O) + electrical flow = Copper Sulfate (CuSO4) & Sulfur dioxide (SO2)

Is powder on your car battery terminals bad?

You bet it is! Copper sulfate and lead sulfate are electrical insulators, so they increase electrical resistance between the battery terminal and battery post, and that increased resistance prevents the alternator from fully charging your battery and also reduces electrical flow to the starter motor. It can also lead to transient current flow (battery drain) even when your engine isn’t running.

Repeat formation of white and blue powder means you have a leak

As mentioned above, sulfuric acid can escape in the gap between the battery case and the post. Once that happens, you will have corrosion problems from that point on. If you clean your battery terminals and posts using the cleaning method shown here and the corrosion returns quickly, you’re got a bad battery. If the battery is under warranty, return it and get a new battery.

There is no way to fix the leaks because the lead posts and plastic case have different expansion-contraction rates.

©, 2020 Rick Muscoplat

Posted on by Rick Muscoplat

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