Is Rotten Egg Smell From A Battery Dangerous [What To Do] 

You find out there is something wrong with your battery as the battery light is on. To check what’s up, you open the hood and spotted a disgusting scent that seemed like rotten eggs.

Now, is rotten egg smell from a battery dangerous?

Yes, the rotten egg smell from a battery is dangerous. This smell is caused by hydrogen sulfide, which is usually derived from the sulfuric acid in the battery. This gas is poisonous and flammable.

is the rotten egg smell from a battery dangerous

So, once you spot this smell, get to a safe distance and proceed with safety equipment such as masks, goggles, and gloves.  

We will be discussing the battery acid smell and what to do in this situation shortly.

Why Car Battery Smells Like Rotten Eggs

To be honest, there is nothing positive about your battery smelling like rotten eggs. The rotten eggs smell comes from the Hydrogen Sulfide gas, which can be created from sulfuric acid. 

car battery smells like rotten eggs

When sulfuric acid is enough heated, it breaks itself down to hydrogen sulfide gas. This can happen in two scenarios-

i) Overcharging: If your battery is overcharged, it can cause the sulfuric acid inside to break down and release hydrogen sulfide gas. So, if your battery smells like rotten eggs when charging, you are maybe overcharging it.

ii) Damaged battery: If your battery is damaged, it can also release hydrogen sulfide gas. This can happen if the battery is cracked, leaking, or has been exposed to heat or chemicals.

So, if you are smelling rotten eggs in your car, you have some bad news. It’s either the battery or the catalytic converter. Either case, you have some maintenance left to do.

But Can A Brand-New Battery Smell Like Rotten Eggs

Yes, a brand-new battery can smell like rotten eggs. All modern car batteries are sold fully charged. So, if you have been charging your car battery and it smells like rotten eggs, it could be that you are overcharging it. 

brand-new battery smell like rotten eggs

If you are not charging the battery and have just had it fitted and get a rotten egg smell, take it back to where you bought it and ask them to check it out or replace it. If the battery emits a rotten egg smell, it could be a sign of a bad battery. 

Is Rotten Egg Smell From A Battery Dangerous

Yes, the rotten egg smell that you are smelling is coming from a very dangerous hydrogen sulfide gas. This gas is flammable and poisonous. So, if you inhale a large amount of this gas you may experience-

  • Eye, nose, and throat irritation
  • Headache
  • Dizziness
  • Nausea and vomiting
  • Confusion
  • Loss of consciousness

In the worst case, you may even die, so you must be extra careful. If you are feeling sick get away from your car and see a doctor immediately. But normally, car batteries cannot generate that much hydrogen sulfide. 

A dangerous fact about hydrogen sulfide gas is, you can smell it at low concentrations. But at high concentrations, when it is actually deadly, you will longer be able to smell it. 

What Do You Do When Your Battery Smells Like Rotten Eggs

You need to proceed with caution if you are smelling rotten eggs from your battery. Follow the steps described below-

what do you do when your battery smells like rotten eggs

i) Ventilate the area: If you are in your garage, then ventilate the area. Open the door of the garage. Try not to inhale the gas too much or you may become sick.

ii) Disconnect and take the battery out: Hydrogen sulfide gas is flammable, which can cause a fire. So, disconnect the battery from the car and take it out. Make sure you wear a mask, gloves, and goggles. To take the battery out make sure you disconnect the negative terminal first then take out the positive terminal.

iii) Neutralize the battery: Before removing the battery, check if it is leaking. If it does, then you will need baking soda and water to neutralize it. Mix 6 tablespoons of baking soda with 4 cups of water. Then spread it over the leaked area. Wait for 30 minutes and now the battery will be safe to remove.

iv) Replace the battery: A leaky or overcharged battery is not safe to use anymore. So, you will have to replace the battery and get a new one. When putting in a new battery, connect the positive terminal first then the negative terminal.

Can You Fix A Battery Smelling Like Rotten Eggs

Usually, it is best to replace a smelly battery, but if you really do not want to part ways with your battery, there might be one or two ways to salvage what’s left.

fix a battery smelling like rotten eggs 

So, if your battery is leaking, there must be a crack or a rupture somewhere in its body. Fixing that leak and replacing the electrolytes will solve the problem with your battery. Or if your battery is overcharged only a little, just replacing the electrolytes will do. 

Here is how you can do that-

  • Before beginning, we assume you have the battery disconnected and away from the car.
  • Prepare a plastic container to transfer the battery electrolyte into. Exercise extreme caution as the battery electrolyte is highly corrosive and can cause harm. If you are not sure how to take the electrolytes out, watch the below video-
  • Smooth out the cracked area of the battery by sanding it with sandpaper until a polished surface is achieved.
  • Apply sealant to the cracked area and allow it to dry for two hours before touching it again.
  • Heat three cups of distilled water to around 150F to recondition the electrolyte. Mix in one cup of Epsom salt and let the solution cool. 
  • Refill the battery with the cooled electrolyte solution and top it off with cold water.
  • If any water is present on the battery surface, thoroughly wipe it off to prevent rust and corrosion. Allow the battery to dry completely.
  • Securely attach new caps to the terminals and ensure they are tightly fastened.
  • For the final step in repairing a leaking automobile battery, charge the battery with a trickle charger for a minimum of 36 hours, giving it a good shake during the charging process.

If you again notice any signs of acid leakage from your car’s battery, have the battery inspected by a professional to address the issue promptly.

Now, if the battery is bloated and/or completely dry, you should give up hope and just get a replacement

What Other Car Parts Can Smell Like Rotten Eggs

There is a possibility that your battery is fine and the rotten egg smell may be coming from another part of the car. So, let’s see what other parts can cause a rotten egg smell in your car-

01. Catalytic Converter

The catalytic converter, a part of the exhaust system, can often give off a rotten egg smell, and it’s actually quite normal. This odor can be more noticeable when you frequently drive short distances without pushing the pedal to the metal. 

catalytic converter

Driving more aggressively occasionally can help eliminate the particles that tend to accumulate and clog the catalytic converter, resulting in the lingering sulfur egg smell.

02. Old Transmission Fluid

Under normal maintenance conditions, old transmission fluid is unlikely to cause a rotten egg smell. However, over time, the additives in the fluid can separate, and the fluid may become dark, and thick, and emit an unpleasant odor.

 old transmission fluid

Your transmission fluid may need attention if you find thick, black fluid and a strong egg smell in the reservoir. Changing the transmission fluid is an affordable task that most DIY mechanics can handle.

03. Fuel System Problems

Gasoline and diesel naturally contain hydrogen sulfide, an element essential for the combustion process. When there’s a breakdown in the engine’s efficiency to burn fuel, you may experience an egg smell coming from the front of the car.

fuel system problems

Two main components of the fuel system can contribute to this smell.

i. Fuel Rail Sensors

When these sensors malfunction, they may misinterpret the pressure and provide inaccurate readings to the car’s computer (ECU). This can lead to the engine receiving more fuel than it can burn efficiently, resulting in partially combusted gases that emit a rotten egg odor. If your car feels less efficient, jerky, or lacks acceleration, these symptoms may also indicate faulty fuel rail sensors.

ii. Dirty Fuel Filter

The fuel filter’s purpose is to catch impurities and imperfections in the fuel before it reaches the engine. However, when the filter becomes clogged or damaged, it can allow impurities to pass through, disrupting the efficient combustion of the fuel and oxygen mixture. While a bad fuel rail sensor is more likely to cause issues with the fuel system, a dirty fuel filter can also contribute to the rotten egg smell.

04. Air Conditioner Blocked

Sometimes, when you switch on the air conditioning after a long period of disuse, you might experience a smell resembling rotting leaves or pine needles.

air conditioner blocked

While this is not exactly a rotten egg smell, it’s a common occurrence in the spring and is often described as a musty odor.

Is It Safe To Drive A Car With Rotten Egg Smell

No, it is not safe to drive a car with a rotten egg smell. The smell is a sign of a faulty battery or other serious mechanical problems. This includes the catalytic converter, fuel pressure regulator, fuel filter, or even the old transmission fluid. The smell is toxic at high concentrations, so avoid sticking your head under the hood and smelling the battery. 

If you are not sure what is causing this, you should take your car immediately to a mechanic.

How To Prevent Your Battery From Smelling Like Rotten Eggs

No one wants their battery to smell like rotten eggs, especially if it can cause some serious health issues. So, here are two simple ways to prevent that from happening-

  • Do not overcharge your battery. That applies to you if you are manually charging your battery with a charger. Usually, it is done by your alternator. So, if your battery is getting overcharged, your alternator may be faulty.
  • To keep your battery healthy, perform routine checks. Looks for corrosion, cracks, leaks, etc. If you find anything like that take steps immediately.


Is it OK to smell batteries?

No, it is generally not okay to deliberately smell batteries. Batteries can emit potentially harmful gases and fumes. Especially when they are damaged or failing. Inhaling these fumes can be harmful to your health. 

What happens if you accidentally smell battery acid?

If you accidentally smell battery acid, you may experience irritation and discomfort in your nose and throat. Battery acid, which contains sulfuric acid, can cause respiratory problems if inhaled. It is important to avoid prolonged exposure to battery acid and seek medical attention if you have any symptoms or concerns.

Does milk neutralize battery acid?

Yes, milk can help neutralize battery acid to some extent. The calcium present in milk will react with sulfuric acid and neutralize it. However, it is more important to rinse the affected area with water immediately. Also, seek medical attention for proper treatment.


Now you know the answer to your question: “Is the rotten egg smell from a battery dangerous?” 

So, you need to exercise caution if you ever find your car battery smelling like this. No matter which component is smelling like this, be careful. Hydrogen sulfide is a toxic and flammable gas that poses risks to your health and safety.

Note: Read our ultimate guide on Why bad alternator diode draining battery.

About John M

John contributed as a technical head at an automobile company just 2 years after his post-graduation in Automobile Engineering. He loves to lead a free life, so he left his job & started blogging. Now, he does research on every automotive problem, part & product and seeks a better solution & best products & shares his findings with his readers to help them as well as to minimize their struggle.

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