Car Battery Smells Like Rotten Eggs – Why?

Did you notice a recent foul odor like that of rotten eggs from inside your car? This is caused by sulphuric acid and other chemicals used to make car batteries. These chemicals produce hydrogen sulfide gas which smells like rotten eggs. This smell can also be referred to as ‘sulfur stink’.

If you have experienced this with your car battery, you can fix it in several ways but first, let’s consider the causes of this smell. 

car battery smells like rotten eggs

Causes of Rotten Eggs Smell From Car Battery

1. Cracked Battery Case 

The cause of this smell has been mostly attributed to a cracked battery case. You should examine the battery case for any cracks if you have left your car idle for a while or have been in storage or packed your car at a long-term parking garage. 

If the situation is true for any of these cases, you must check that your battery connections are tight or there is no corrosion in the terminals. 

If your battery connections are loose or there’s corrosion in your terminals, there will be a leak of sulfuric acid on the heated metal parts of the battery box and that will cause a foul smell as well as more corrosive damage. 

2. Bad Catalytic Converter 

The catalytic converter is filled with carbon compounds that burn off whenever the car engine is cranked up. 

What this means is that the carbon transforms into hydrogen sulfide in the car’s exhaust and this is sent back into your car’s interior which gives off the rotten egg smell. 

Often, this happens because of a lack of maintenance from the car driver or owner, such as not checking the catalyst under the hood before turning on the headlights and driving at night. 

To inspect the catalytic converter, check under the hood for an inspection port near the emission equipment if you have one, as there should be one near it. 

3. Transmission Fluid Leakage

Another cause of this car smell is the transmission fluid leakage. Inspect your transmission fluid line. There may be a small leakage that might have been caused by wear and tear from being used over time or age. 

This can happen when you’re accelerating quickly or driving up a hill as that’s when the transmission fluid pumps faster which results in making your car hotter than normal. The metal parts of your car engine can also cause this leakage if it spins too fast due to increased RPM. 

If any of this happens, it will cause the car to become hot and break down the oil into sulfuric compounds which produces that bad egg odor that will fill your car. If your transmission fluid remains tightly sealed and you don’t have any leakages, your car won’t smell like rotten eggs.

Car Battery Smells Like Rotten Eggs – Solution

As I stated earlier, the sulfuric compound in your car battery is the cause of the bad egg odor. This is the chemical that ensures that the car battery works. It’s not a good sign if the battery gives off this odor. Especially when there are signs of corrosion on the terminals.

If you notice this smell from the interior of your car, check on the car battery terminal for corrosion, and wipe it off with a toothbrush soaked in baking soda or vinegar. Use water to rinse off the debris. Clean it off and allow it to dry. 

When the terminals are dry, apply some petroleum jelly on the metal parts to seal out any form of moisture then reconnect your cables to the terminal for electric flow to continue to the circuit starter. This should fix the rotten egg smell if the cause is due to corrosion on the battery terminal. 

If the situation is due to another effect inside the battery like a crack, you might have to replace the battery entirely to stop this smell. 

If a faulty catalytic converter is the cause of the problem, you cannot solve this issue any other way except by replacing the converter of your car. 

If the cause of the problem is a transmission fluid leak, you have to find a way to patch that leakage or replace the transmission fluid line.

Is The Rotten Eggs Smell From A Car Battery Dangerous?

Fortunately, it isn’t dangerous. Batteries emit a foul odor caused by sulfuric acid, which smells like hydrogen sulfide or bad eggs. Your car battery loses its charge over time due to the deterioration of the lead-acid chemicals inside of it.

As a general rule, this smell does not mean anything serious is wrong with the car battery. It just indicates poor maintenance.

However, it can also be caused by a malfunctioning battery due to an imbalance in the contents of the battery, caused by a leak or crack in the car battery. Such instances can be dangerous. 

This is why you shouldn’t ignore this kind of problem and act immediately if you perceive any bad odor coming from the engine bay or interior of your car.

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A battery check is a good idea if you perceive an unpleasant smell. You should also get a test done at an auto parts store for free, and they will proffer reliable solutions on how you can handle the matter. Battery terminal corrosion reacting with other materials under the hood is a common reason why your car battery smells like rotten eggs. Simply replacing the battery will solve the problem.