Battery Smells Like Rotten Eggs – Causes & Fix

A rotten egg smell is one of the most annoying and uncomfortable smells you will perceive from your car. This uncomfortable odor will leave you wondering if you, by any means, leave eggs somewhere in the car. Believe it or not, most times, the rotten egg smell comes from the battery.

It can also come from a bad catalytic converter, forgotten food remnants, and damaged exhaust system components. These are topics for another day. But in the course of this article, I will explain why your car battery smells like rotten eggs and the dangers of inhaling the unpleasant odor.

12 volt battery smells like rotten eggs

Why does my car battery smell like rotten eggs

Marine batteries, lawn mower batteries, golf batteries, forklift batteries, car batteries, and other lead-acid batteries are all capable of smelling like a forgotten rotten egg smell in the car.

These lead-acid batteries have two lead plates — submerged in sulfuric acid. The battery produces power to start the car and run other electronic components by exchanging electrons in chemical reactions between the sulfuric acid and the lead plates.

As the battery runs out of charge, it produces sulfate. When you recharge the battery, the sulfate dissolves inside the battery again. If you do not recharge the battery for a very long time, the sulfate will stick to the lead plates, reducing the battery’s efficiency and lifespan.

The sulfate in the battery will react with damp air, creating the rotten egg smell you perceive from the car battery.

Generally, the most common reasons why an old or brand-new battery smells like rotten eggs are overcharging, overheating battery, leaking battery, and using a defective battery charger.

Overcharged battery

Generally, if your battery smells like sulfur when charging, quickly unplug the battery. When charging a car battery, a sulfuric or rotten egg smell shows that the battery is overcharged. Most often, the common reason why you perceive a rotten egg smell when charging your battery is that you are using an oversized charger.

Overheating battery

Do you remember that I said lead-acid batteries are produced with two lead plates submerged in sulfuric acid? I guess you do. The battery will overheat if there isn’t enough acid covering the lead plates.

During the overheating, the sulfuric acid in the battery will turn into a gas form of hydrogen sulfate, causing the rotten egg smell you perceive. A common sign that indicates you have an overheating battery is a swollen battery case.

Leaking battery

Another reason for a rotten egg smell from a car battery is leaks. Under regular operation, chemical reactions happen inside the battery — causing an awful egg smell, but the odor becomes obvious when the acid leaks.

If a car battery leaks, it will release sulfuric acid (H2SO4) and hydrogen gas (H2). If the sulfuric acid and the hydrogen gas mix or touch any component that contains sulfuric material, such as rubber, it will form a hydrogen sulfide gas (H2S). Of course, hydrogen sulfide gas is known for its rotten egg smell.

Using a defective charger

Charging your car battery with a defective charger will either cause the battery to overheat or overcharge — leading to the production of hydrogen gas (H2), which will cause hydrogen sulfide gas (H2S) over time.

A hydrogen sulfide gas is very dangerous and has harmful effects and a distinct rotten egg smell. So, if your battery smell when charging, you are most likely using a bad charger.

Is the rotten egg smell from a battery dangerous?

A rotten egg smell from car battery can be very dangerous in a ventilated area if the smell is too much. The rotten egg smell can cause severe throat and sinus irritation. Therefore, do not inhale it for any reason to avoid health issues.

What happens if you drive with rotten eggs smelling battery?

Rotten eggs smell from a car battery shows there’s an issue with the car battery that needs urgent attention. Most times, you only perceive the smell when there’s a chemical reaction in the battery that is producing a hydrogen sulfide gas.

Inhaling rotten eggs smell from a car battery will cause nausea, headaches, and tearing of the eyes. It’ll also affect your car performance because ignoring it for long will cause further issues to the battery and other electrical car components.

battery smells like sulfur when charging

How do you fix rotten eggs smell battery?

Whenever you perceive a rotten egg smell from your car battery under regular use, the best thing to do is to replace the battery. The foul smell shows the battery is overheating or can’t recharge properly.

But if your caravan, semi-truck, car, or tractor battery smells like rotten eggs when charging, you’re most likely using an oversized or defective charger. Check the charger and ensure it is the recommended size for your vehicle. If it is the right size, check if the charger is in good condition. If the charger is not the right size or it’s bad, replace it accordingly.

Frequently Asked Questions — FAQs

Will a leaking battery smell like sulfur?

The short answer is it depends. A leaking battery can smell like sulfur if the leak is caused due to overheating, overcharging, or chemical reactions inside the battery. But if the leak is caused due to cracks, it will only emit a chemical or acrid smell.

Can the smell of battery acid hurt you?

People have different opinions on this. Some argue that injecting a small amount of battery acid will not hurt you, but the truth is — injecting even the smallest amount can be dangerous. Therefore, I recommend you avoid it at all costs. If you swallow or inhale too much battery acid, it will cause you nose and throat irritation, headaches, cough, difficulty sleeping, and decreased mental ability.

Can you drive with a leaking battery?

While a leaking car battery may not prevent you from driving, do not drive with it. The leak from the car battery is unsafe for you, the vehicle, and the atmosphere. The sulfuric acid from the battery can also cause corrosion on any engine parts it touches. If you were asking, is it safe to drive a car that smells like rotten eggs? Now you know.

What happens if you touch a leaking battery?

Do not touch a leaking battery. Touching it will cause burns or skin irritation. However, this type of burns will not come right away. It will take several minutes or hours before you notice the burns. If you touch a leaking battery, wash it off immediately with cold water.

Is a battery still good if it leaks acid?

Using a battery that is leaking acid is not recommended because it poses safety hazards. And please, don’t throw your leaking battery away so it won’t end up in landfills and leak the acidic gas into the environment. Ensure you recycle it properly.

Final Words

Lastly, if your car battery smells like rotten eggs, it’s time to get a new one. The stinking odor is highly toxic if inhaled in large quantities. So, do not sniff the battery to confirm if the rotten egg smell is coming from it.

Instead of sniffing, watch out for cracks and watery substances on the battery, or better still, contact your mechanic to replace the battery.

Osuagwu Solomon

Osuagwu Solomon is a certified mechanic with over a decade of experience in the mechanic garage, and he has over five years of experience in the writing industry. He started writing automotive articles to share his garage experience with car enthusiasts and armature mechanics. If he is not in the garage fixing challenging mechanical problems, he is writing automotive repair guides, buyer’s guides, and car and tools comparisons.

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