Why Car Battery Smells Like Rotten Eggs? Easy Fix!

You may have noticed that the battery in your car smells like rotten eggs. The reason is because of sulfuric acid and other chemicals used to make the battery. These chemicals can create hydrogen sulfide. This gas will emit an odor that some people describe as smelling like rotten eggs or garlic – hence the name “sulfur stink.”

car battery smells like rotten eggs

The good news is there are ways you can fix this problem!

Find the Source of Smell

Many times, the smell emanates from a cracked battery case. This is especially true if you have had your car in storage for some time or it’s been left idle at an airport parking lot or long-term parking garage while traveling.

In these cases, check to see that all connections are tight and make sure there isn’t any corrosion around the terminal posts – this can lead to leaking of sulfuric acid onto heated metal components inside the battery box which will create more odor as well as cause corrosive damage.

It can be a Bad Catalytic Converter

The other possibility is a failing catalytic converter. This device gets clogged with carbon deposits and when you crank up the engine, these get burned off – which means they turn into hydrogen sulfide gas in the exhaust system that then drifts back to your car’s interior where it smells like rotten eggs or garlic.

This can be caused by a lack of maintenance for this part too, such as not inspecting the catalyst underhood before each use of headlights while driving on dark roads at night. If you have an inspection port beneath the hood near emissions equipment there should be one somewhere close to it so check around!

Transmission Fluid Leak Can Also Cause Rotten Eggs Smell

This could be another possible cause for your car to smell like rotten eggs. You may have a small leak in the transmission fluid line, which can happen because of age or just from normal wear and tear over time.

This will sometimes make your car run hotter than usual – more so if you’re driving up steep hills or accelerating quickly – as this is when the transmission fluid pump circulates at its highest speed. The metal parts inside the engine are also spinning faster due to increased pressure on them with an increase in RPMs, too! When either one happens, it’ll create heat that causes the oil within these components to break down into sulfur-containing compounds that then produce odors strong enough to fill your vehicle with bad smells.

Unless you have a leak in the transmission fluid, you won’t smell such odour as the transmission fluids remain well-sealed.

How to Solve the Rotten Eggs Smell in a Car Battery

The smell of rotten eggs is usually attributed to sulfuric acid. This is the chemical that makes your car battery work, so it’s definitely not good if there are signs of corrosion on the terminals and you have this odor coming from them.

To fix this problem, one should clean off any corrosion with an old toothbrush dipped in baking soda water or vinegar (which will also neutralize the smell) then use fresh water to rinse everything away.

Once dried thoroughly, give all metal parts a light coating of petroleum jelly which will seal out any moisture before reconnecting the cables to maintain electrical flow through your engine starter circuit. After completing these steps, take a deep breath because now you’ll be able to enjoy your car with a fresh, non-sulfurous smell.

However, this fix may not work always as the smell may come out due to a malfunction inside the car battery. In such cases, it is better to replace the car battery with a new one.

If the issue is with the bad catalytic converter, there is no way to solve the issue without replacing the catalytic converter of your vehicle.

And when it is caused by a transmission fluid leak, the leak must be patched for a permanent solution.

Why Car Battery Smells Like Fart?

The smell of farts is a sure sign that the battery needs to be replaced. The high acid levels in your car’s battery cause this odor as it breaks down and leaks into the air vents. It could also mean that there is some kind of leak inside the car, such as gas fumes entering through an open window or fuel lines from a ruptured tank leaking out onto other parts of the engine bay.

Is the rotten egg smell from a battery dangerous?

It is not dangerous. The foul odor from a battery is sulfuric acid, which smells like hydrogen sulfide or rotten eggs. It’s caused by the breakdown of lead-acid chemicals in your car battery as it discharges electricity and loses its charge over time. In normal circumstances, this smell doesn’t indicate that there are any serious problems with the car battery itself or anything else on your vehicle – just poor maintenance.

However, in some situations, it may be caused by a leak or crack in the car battery or malfunctioning battery due to the imbalance of contents inside the battery. In such cases, it may become a grave issue. That’s why we recommend not to ignore this kind of issue and act promptly when you smell a bad odor in the engine bay.


It’s a good idea to have your battery checked if you notice the smell. Most auto parts stores will test for free and give some recommendations on how to fix it.

In many cases, the cause of this odor is a corroded battery terminal chemically reacting with other materials under the hood. Changing the battery should solve the problem without any hassle.

If you continue to experience these symptoms after changing out your battery, there may be other issues like a bad catalytic converter or transmission fluid leaks.

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