Can a Car Battery smell like Rotten Eggs? What to do?

If you’ve ever opened the hood of your car and been hit with the distinct, unmistakable smell of a rotten egg, it’s likely your car battery is the source of the problem. The smell, technically known as “hydrogen sulfide”, can be a sign of a serious fault with your battery, and needs to be addressed to prevent further issues. 

This foul odor can be both embarrassing and unpleasant, and can potentially impair the performance of your car’s electrical system. 

However, you don’t have to panic; there are simple steps you can take to try to fix your car battery with a rotten egg smell coming from it. But before getting started, keep in mind that safety is always a top priority; it’s important to know how to properly handle a car battery and use appropriate safety equipment when dealing with any type of electrical repairs.

What Causes a Car Battery to Smell Like Rotten Eggs?

There could be several causes that lead to a stinky battery, but the most common is a buildup of sulfates and the release of hydrogen sulfide. This smell is a by-product of the chemical reaction going on inside the battery between sulfur, lead, and water. It is normal for minor amounts to be produced, however, it can build up if not addressed. This buildup, as well as other physical signs, can be a warning sign of a faulty car battery.

Why do sulfates form in car batteries?

Sulfates often accumulate when sulfuric acid, a component of a car’s battery, mixes with other metals like copper and lead inside the battery. This causes the battery to overheat and leads to a chemical reaction that produces hydrogen sulfide gas. Hydrogen sulfide gas is what gives off the smell of rotten eggs, and can potentially lead to serious battery damage.

There are several reasons why sulfates may form in a car battery, but the most common are overcharging, undercharging, not installing the battery correctly, or leaving it for too long without maintenance. If you do not properly maintain the battery, it can cause the battery acid to corrode the internal parts, leading to the release of hydrogen sulfide. Another common issue is short-circuiting, which can happen if the battery terminals are not properly insulated or if battery acid is spilled onto the connections.

What To Do When Your Battery Smells Like Rotten Eggs?

If you smell hydrogen sulfide coming from your battery or any other sign of a faulty battery, it is important to get it fixed as soon as possible. If you catch it early enough, simply checking the connections and making sure everything is tightened can do the trick. However, if the smell persists or is particularly strong, it is best to inspect and replace the battery. If the battery is overcharged, you will need to replace it with a new one.

Find the source of the smell first 

First, you’ll want to determine if the smell is actually coming from your car battery or if it is something else. If the smell is associated with other engine issues, such as poor performance, it’s likely the smell is caused by something other than the battery. However, if no other problems are present and the smell persists, then it’s likely coming from the battery.

Once you are sure that it’s coming from the battery, you’ll want to inspect its condition to make sure it’s still in working order. If your battery is old (more than five years) or doesn’t have an adequate charge, it’s likely that you will need to replace it.

Clean the battery and the area around it. 

It’s important to remove any dirt, grease, or corroded material in order to minimize the smell and the risk of electrical problems. Start by disconnecting the battery and wiping off any visible dirt. Then, use baking soda and a damp cloth to scrub the battery and the surrounding area. If the smell persists, you can also try using a commercial cleaner like a battery terminal cleaner, but make sure you double-check that it’s safe to use on your battery before you start.

Make sure the battery is dry 

Once the battery terminal area is clean, you have to make sure it’s completely dry. The moisture present in any unclean areas could react with the battery terminals and cause further corrosion and even a fire. Before reattaching the battery terminals, layer waterproof grease on the terminals and battery cables. To finish up, reconnect the cables and secure them in place.

Is the Rotten Egg Smell from a Battery Dangerous?

Hydrogen sulfide is a toxic gas, and inhaling it can lead to a number of health problems, including coughing, trouble breathing, and even vertigo. In high concentrations, it can also be fatal, so it should not be taken lightly.

In addition to health issues, sulfates can also cause corrosion and damage to the battery plates. This damage can cause the battery to become inefficient at holding a charge, or in some cases, no longer be able to retain a charge at all.

What To Do When A Car Smells Like Rotten Eggs And Won’t Start?

If your car won’t start and you smell a pungent odor that resembles rotten eggs, there are several possible causes that need to be checked. Before attempting any diagnostics, make sure the car is in a safe environment and the parking brake is engaged. Now use a voltmeter to test the voltage of the battery. If the voltage is below 12v, then the battery is likely dead and needs to be replaced.

Check the Alternator First 

If the battery voltage is above 12v, then the alternator needs to be checked. The alternator’s job is to keep the battery charged by converting mechanical energy from the engine into electrical energy. To check the alternator, use a voltmeter to test the voltage output of the alternator. If the voltage measured is below 12v, then the alternator is likely faulty and needs to be replaced.

Now Check the Fuel System

If both the battery and the alternator are functioning properly, then the issue may lie within the fuel system. This could mean a clogged fuel filter, fuel pump failure, or a leaky fuel injector. 

How to Check 

First, remove the fuel filter and inspect it for debris or contaminants. If the fuel filter looks clean and unrestricted, then the fuel pump and fuel injectors need to be tested next. 

To test the fuel pump, use a fuel pressure gauge to check the pressure of the fuel system from the pump. If the fuel pressure is below the manufacturer’s specifications, then the fuel pump needs to be replaced. 

Use a multimeter to check for a voltage drop in the injectors when the engine is running. If there is a voltage drop, then the fuel injectors need to be replaced.

Check the Exhaust System

If all of the components mentioned above check out and the car still won’t start, then the exhaust system may be the culprit. This could be caused by a clogged catalytic converter or an exhaust leak. 

How to Check 

To check the catalytic converter, remove the exhaust from the engine and inspect it for any blockages. If the catalytic converter appears to be clear, then an exhaust leak may be to blame. To check for an exhaust leak, use a vacuum gauge to check the vacuum pressure in the exhaust system. If the vacuum is low, then there is a leak in the system and it needs to be repaired.


When it comes to maintaining your car’s battery, it’s important to pay attention to any suspicious smells that might be emanating from it. One smell you might notice is the smell of rotten eggs or hydrogen sulfide. If you detect a smell like rotten eggs coming from your device’s battery, don’t try to continue using it. This is a sign that something is wrong with the battery, and you risk potentially damaging it further if you continue to use it. Immediately remove the battery from your device and try to locate where the smell is coming from. If the smell is coming from the battery then try to clean it as we have instructed here and see whether the smells persist or not. If the smell still persists, the best course of action is to replace the battery. 


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