‘Take It To AutoZone’: Toyota Has Severe Battery Corrosion After Only 9 Months. Then A Mechanic Spots Something Shocking

"What would cause this?"

Man Posts About Severe Battery Corrosion After Only 9 Months. Mechanics Immediately Point To A Bigger Problem

Photo by: Erik Mclean & michael

Stacy Fernandez

By: Stacy Fernandez

Feb 22, at 4:00pm ET

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When your car won't start, popping the hood is usually step one. But sometimes what you find under there raises more questions than answers, especially when the battery is practically brand new.

Redditors were surprised to see the condition of a battery and had thoughts about what could have caused such an issue so quickly.

Why Does The Battery Look Like That?

A Reddit user posted to r/AskAMechanic with a problem and a photo that had mechanics doing a double-take. Their 2009 Toyota Yaris had been running great since they replaced the battery nine months earlier.

Then one day, it powered on but wouldn't crank the engine. When they opened the hood, they found the battery terminal buried under a thick layer of crusty, fluffy white-green corrosion. It’s the kind of buildup that can happen after years, not months.

"What would cause this amount of buildup in 9 months?" they asked.

The post also made its way to r/AutoZone2 under the title "Free Battery Testing"—a nod to the fact that most people facing this issue would head straight to AutoZone for their complimentary battery and alternator testing. However, some self-identified AutoZone employees in the comments suggested they might be on their own.

“We can't because of corrosion build up,” one wrote.

AutoZone’s site does not appear to address the issue of whether it tests batteries with severe corrosion.

What Did Mechanics Say?

The mechanics of Reddit were quick to point out that this much corrosion in such a short time isn't normal and it's usually a sign of something bigger going on.

According to one commenter, heavy corrosion on the positive terminal is often a symptom of overcharging. Another pointed out that cheap batteries are a common culprit, or that the alternator might be putting out too much voltage.

Some mechanics noted that other factors could contribute—like lots of short drives that don't give the battery time to fully charge, or a parasitic draw draining the battery when the car is off. But the consensus was clear: corrosion this severe, this fast, usually means the charging system needs to be tested.

"Take it to AutoZone or Advance [Auto Parts] and have the battery and the alternator tested. Replace the battery if it tests bad. Most batteries come with a warranty. If the battery is bad, take it to where you bought it and do a warranty replacement," a person suggested.

What Causes Battery Corrosion?

According to Jiffy Lube, battery corrosion happens when the sulfuric acid inside a battery releases small amounts of gas. When that gas contacts the metal terminals, it reacts with oxygen in the air to form sulfuric acid crystals (that’s the white, grey crusty buildup you see in the photo).

Over time, this corrosion becomes a poor conductor of energy, which means your battery can't function the way it should. You'll notice slow cranking, dim lights, clicking sounds when you turn the key, and eventually a dead battery.

But corrosion on the positive terminal is often a sign of something more serious.

According to Battle Born Batteries, heavy corrosion on the positive side is frequently a symptom of overcharging. That means the alternator is putting too much voltage into the battery, which can happen when the voltage regulator is failing.

Overcharging doesn't just cause corrosion. It actively cooks the battery, shortening its lifespan significantly. The average car battery lasts four to six years under normal conditions, but corrosion and overcharging can cut that short.

How Do You Clean A Battery?

If you're dealing with corrosion like this, the fix itself is pretty straightforward. According to both Jiffy Lube and Battle Born Batteries, here's what you need to do:

What do you think?

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Safety first. Make sure the engine is off and has cooled down. Always wear goggles and rubber gloves
Disconnect the cables. Negative first, then positive
Mix your cleaning solution. A tablespoon of baking soda into a cup of hot water
Scrub it down. Dip an old toothbrush (or a wire brush designed for battery terminals) into the mixture and scrub away the corrosion. The baking soda neutralizes the acid, and you'll see it fizz as it works
Wipe and dry. Clean everything with a rag and let it dry completely
Reconnect. Positive first, then negative
Prevent future buildup. Coat the terminals with dielectric grease or Vaseline

One important note: don't use Coca-Cola like some people suggested. While it might clean the corrosion, it also makes your cables delicious to rats, who will absolutely chew through your wiring. Stick with baking soda, and remember, if the underlying charging issue isn't fixed, the corrosion will just come back.

Motor1 reached out to the original poster via Reddit for comment. We’ll update this if they respond.

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