What Causes Car Battery Smells Like Rotten Eggs?

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As you returned from the long trip last night, you pulled over inside the garage and went straight to bed.

Upon waking up and entering the car to unpack your things, you noticed a putrid smell like that of rotten eggs.

You know that you never left any eggs in your vehicle or inadvertently left the car open for anyone to throw anything into it.

But you keep wondering where this stinky smell emanates from in the car?

If you don’t have any issues with your smelling organ and the catalyst converter of the vehicle isn’t broken, the immediate suspect is the car battery.

What can cause the car battery to smell?

Before I answer the question, let me say that you can easily detect a damaged catalyst converter by smelling the exhaust fumes.

Having said that, let me explain what causes the car battery to give a rotten egg smell.

What Causes Car Battery Smell Like Rotten Eggs?

Typically, your car battery gives off a sulfuric or rotten egg smell when it releases hydrogen sulfide.

Another crucial reason is overcharging. The battery contains sulfuric acid and electrolyte water.

So, when you detect the rotten egg odor, the battery has become overheated, causing the conversion of the sulfuric acid (electrical) to hydrogen sulfide gas (chemical).

This electro-chemical conversion leads to a stinky smell.

Let me start by explaining how a car battery works.

The lead-acid battery produces a lot of energy during the internal combustion process.

This process allows the battery charger to cause exchange of electrons between sulfuric acid (H2SO4), lead-oxide plates, and lead plates.

As a result, the electrical current will pass through the battery’s electrolyte solution.

The process culminates in converting electrical energy in the charger into chemical energy in the battery.

This conversion process can only take place and be complete if the battery is charging at an average rate.

Now, you understand the mechanism of your car battery.

When the car battery discharges, lead sulfate is produced.

The sulfate can stick to the lead plates, causing the sulfuric acid to react with damp air. The result is a formation of a disgusting rotten egg smell.

So, let me tell you how the rotten egg smell is produced.

There’s a consequence of leaving the battery to charge for an unnecessarily long time or storing it at high temperatures.

It will cause the lead sulfate to form in your battery. Of course, the battery performance and life will reduce.

How To Remove Rotten Smell From Car Battery

Let me state that you’ll need to adhere to all safety precautions down the way.

Never think that the smelling car battery is no longer fit for use.

No, you can take steps to safely remove sulfation from the battery and make it suitable for the vehicle.

The process will cause the battery to trickle-charge and overheat, thus emitting dangerous acidic substances while igniting hydrogen gas.

Depending on the size of your battery, desulfation may take 48 hours to a week to complete.

Supplies needed:

  • Battery electrolyte
  • Voltage meter
  • A resistor (2Ohms)
  • Alligator clamps
  • Wires (2)
  • A Current meter
  • DC lamp (400-Watt) (you can use an AC (400-Watt) with a power inverter
  • A car battery charger

Step-By-Step Guide To Desulfate Your Battery

Step 1: Pull Out The Battery

To start, disconnect the battery terminals from the clamps and remove the plastic covers from the battery cells.

Depending on the battery’s voltage, the covers can be between three and six. Ensure you disengage the black-colored negative cable first before the red-colored positive end.

After this, pull out the battery from its rack.

Step 2: Connect The Battery Cable To A Resistor

Start by connecting the red-colored positive battery end to a resistor.

Connect the battery’s two ends to a resistor with the alligator clamps. Fix the resistor to the current meter before joining the positive and negative heads to their respective ends of the charger.

The battery is now ready for an overcharge.

Step 3: Allow Terminal Voltage To Rise

After connecting the charger and resistor, allow the battery voltage to surge to about 2.6 volts per cell, turning on the charger at 51volts.

The battery current meter should be at zero or close to this voltage.

The current will be stable at between 10Amp or 20Amp after rising steadily for a few hours.

Step 4: Allow The Battery To Overcharge

Allow the battery to charge for several hours, up to 48 hours.

You’re targeting to have at least 12 volts of charge on the battery.

If the voltmeter reads 12V or more, then disconnect the charger. If not, continue charging for further hours.

If the battery cannot get to 12V after 96 hours of charge, it’s time to dispose of and replace it with a new one.

Step 5: Store Battery And Check Voltage

After disconnecting, store the charged battery for around 24 hours.

After, use your voltmeter to check if the voltage drops to 11V.

If it falls, the battery isn’t good for your car. It’s time to discard it.

Step 6: Cycle The Battery

Now that you’ve trickle-charged and overcharged the battery, it’s time to recover the battery voltage cells.

This stage involves discharging and recharging the battery. This is what is called ‘battery voltage cycling.’

Start by discharging the battery and disconnecting once it gets to 11V. Your car headlights or lamps should do the magic.

Recharge again until your battery voltage hits 12.5V. Repeat the discharge and recharge steps.

However, each step should increase the length of time the battery lights the headlights.

Step 7: The Battery Is Perfect

Once the repeated processes ensure that the cycling no longer significantly reinforces the durability of the battery, then your battery is desulfated and ready for use.

What To Do If You Notice Rotten Egg Smell?

What should you do when you notice this dangerous smell from your battery?

When you detect the rotten egg-like odor, the best and foremost thing to do is disengage the battery from service.

Since there is at least one damaged cell in the battery, you cannot continue to use the car battery.

If you do, you’ll be putting excessive strain on the other cell and causes both cells to fail.

In addition, leaving the battery will cause the emission of dangerous hydrogen sulfide gas, which can irritate the sinuses and contaminate the work environment.

You’ll also want to avoid the toxicity of sulfide gas that can affect your body organs.

But first, you should avoid breathing in the battery sulfate or inhaling the pungent odor.

The good thing is that H2S doesn’t produce any odor at higher concentrations.

Once you pull off the battery, contact a certified battery service technician to inspect the battery.

After looking at the capacity, condition, make, and age of the battery, the professional should be able to advise whether you can fix the battery or replace it.

They’ll be able to tell the extent of the damage: which cells are still active and which ones are dead.

Is The Car Battery’s Rotten Egg Smell Hazardous?

Yes, whether at a low or high concentration level, hydrogen sulfide gas is hazardous to human health.

H2S can cause, at the least, loss of consciousness at low concentration.

It can also affect the respiratory system and trigger skin, eye, or throat irritation.

In extreme cases, the gas can lead to death.

Final Considerations

The battery is essential to the quality of performance of the vehicle.

It converts the electrical energy to chemical energy and vice versa.

The rotten egg smell your car battery produces can harm your health and the vehicle.

This is why you need to pull the battery out of service once you detect the odor.

Ensure you regularly check your battery.

Truth is, not every condition of a failing battery results in a rotten egg smell. As I noted earlier, a terrible egg odor doesn’t always indicate a bad battery.

There are other reasons you may detect the rotten egg smell. You’ve got to always be on the lookout for every sign from the battery.