Why Does My Car Battery Smell Like Rotten Eggs?

You’ve just sat in your car and noticed a strange smell similar to that of rotten eggs. Yet you know you haven’t left any in it or had someone throw some at it. So just what is causing this awful stink?

Believe it or not, that awful smell could be coming from your car’s battery. But there may be another reason for this smell getting produced.

The main one is that the battery is overcharging and causes the production of sulfur gasses.

However, if the smell is coming from the car’s battery, you will need to take action quickly. Otherwise, you could face other problems such as a dead battery.

What Causes Batteries To Smell Like Rotten Eggs?

Most cars will use a lead-acid battery to start the engine and run electrical components in it. These batteries get filled with electrolytes comprising H2SO4 (water and sulfuric acid).

When a battery goes through the charging process, sulfur (H2S) gets generated, which results in you noticing a smell like rotten eggs as you get in your vehicle.

Below we will take a look at the reasons why the battery of your car is producing this smell.

The main reason why your battery smells like rotten eggs is overcharged battery.

Overcharged Battery

Should one or more of the cells within the battery in your car fail, when you go through the charging process, the charge voltage gets divided between the cells that are still working?

In turn, this leads to them becoming overcharged and drawing excessive currents. As a result of this, more sulfur gas gets then generated.

The best way to check if any cells in your car’s battery have failed is to do the following:

  • Are certain parts of the battery getting hotter compared to other parts? You can use an infrared thermometer to find which cells have failed.
  • Have you noticed that when you impose a small load on the battery after it has been charged? If it is weak, you get a much lower voltage reading.

If you notice any such issues, you must replace the battery as soon as possible. You may also want to consider desulfating the battery, but it will not restore it to full working order.

RELATED: Can You Overcharge A Car Battery: Reasons and Tips for Charging

Dead Battery

This rotten egg smell may result from acid leaking into the battery and is a clear sign that the battery is dying or is dead. Again the best thing to do is replace the battery as soon as you notice the battery isn’t working as well as it should.

Low Electrolyte Levels In The Battery

Overcharging of the battery can cause the levels in it to become depleted. The lead plates inside the battery will become exposed.

When the hydrogen gas comes into contact with the sulfates on the exposed lead plates, hydrogen sulfide gas gets produced. 

To prevent this, you need to make sure that you keep your car’s battery topped up with distilled water.

Problem With The Catalytic Converter

Should the catalytic converter on your car become damaged or worn out, this will cause hydrogen sulfide gas to leak out. The only way to rectify this problem is to have a new catalytic converter fitted to your vehicle.

A Frozen Battery

Should the battery in your car become frozen, it may cause it to vent gas, which is when the rotten egg smell appears. You need to defrost the battery, ensuring that it has wholly defrosted before plugging it into a battery charger. But before you do this check, the battery case to make sure there aren’t any cracks, or it hasn’t got broken.

Can A New Battery Smell Like Rotten Eggs?

A new battery can produce a smell similar to rotten eggs and is usually caused by the same reasons discussed above.

But also it could be because the battery isn’t connected correctly. This is something that can occur to the batteries used in golf carts.

Is A Battery That Smells Like Rotten Eggs Dangerous?

If you do notice the battery smells like rotten eggs, then you must deal with this as a matter of some urgency for the following reasons:

  • It could be a sign that your battery is about to die, leaving you stranded on the side of the road
  • The risk of a fire occurring is high as H2S compounds are flammable and can explode when they come into contact with air
  • It can cause you health problems when exposed to low concentrations of H2S compounds. It can lead to problems with your respiratory system or your corneas. Higher concentrations can cause paralysis of the olfactory nerves.
    In turn, it leads to unconsciousness and can lead to sudden death.

What Do You Do To Avoid A Battery Smelling Like Rotten Eggs?

battery smells like rotten eggs
3 tips to avoid having a rotten egg smell from car battery.

To avoid your car’s battery smelling like rotten eggs, you can do several things.

  • Carry out regular checks of the battery, both the cells and the electrolyte levels in it.
  • Avoid leaving your car outside in cold weather for too long to prevent the battery from freezing.
  • It is worth buying a smart charger to help prolong the battery’s life. Today there are plenty of smart chargers you can buy that come with desulfation and recovery modes. Both of which will help to desulfate and recondition your battery for you automatically.

You may want to consider investing in three such batteries that come with the desulfate mode as standard on them: the TowerTop Battery Charger, the Schumacher SC 1281, and the Noco Genius S2X2.

See TowerTop Battery Charger, Schumacher SC 1281, Noco Genius S2X2 here:

TowerTop Battery Charger

TowerTop Battery Charger


Schumacher SC 1281

Schumacher SC 1281





RELATED: OPTIMATE 6 vs CTEK 5.0 vs NOCO GENIUS5: Which most home mechanics are using to recondition batteries?


As soon as you start to notice that your car’s battery smells like rotten eggs, you must find out what the cause is. Once you’ve found the reason, you can then rectify the problem.

However, you should notice this smell, and you need to rectify the issue sooner rather than later. A weak battery isn’t a dead one at this time, but it will quickly become one if you don’t sort the problem out as soon as you can.

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