6 Reasons Why Your Car Battery Is Smoking And Releasing Toxic Fumes

A smoldering and smoking car battery can be a confusing thing for even the most experienced drivers and even mechanics. It is rare that a battery starts smoking and releasing toxic smoke and fumes that smell like rotten eggs. Yes, like rotting eggs. A typical car battery is based on acid, and electrolytes and it contains plates made out of lead and other materials. Those plates are submerged in a solution of electrolytes that contains about ⅓ sulfuric acid and ⅔ water. As the battery starts smoking, what you smell is evaporating sulfuric acid that has a scent similar to smoking eggs.

Enough talking about rotting eggs, let us get into why a car battery starts smoking and smoldering in the first place!

Reason Why Your Car Battery Is Smoking

There is not a simple, universal reason why a car battery would suddenly start smoking. The reason might lie in the battery itself, in poor maintenance work on the car and even the environment has a big part in it. Here are the 6 reasons for a smoking car battery.


Let us kick things off with the most common reason for a smoking car battery, it is overheating. During the summer season, the number of reports of smoking car batteries almost triples and it is all because of the summer heat. The excessive heat takes a toll on the battery and what happens is the electrolytes (the liquid part of the battery) inside the battery actually start evaporating and as you can imagine, it looks like smoke.

To avoid overheating the battery you already have, make sure you turn it off and cool off your car in shade. Continuing to force a smoking battery to work will only result in the battery failing completely in a matter of minutes. While some people do recommend insulating the battery compartment with DIY insulate materials, most cars have no space around the car battery, or even worse, the wrong choice of insulation materials leads to even more heat being trapped in and around the battery.

If you live in an area with a hot climate or extreme temperatures in the summertime, the only right thing for you is a new car battery that is suited for extreme heat. These car batteries offer better isolation and heat dissipation through ventilation and work perfectly in such conditions.


Using a battery charger is not something anyone should be doing, especially without the necessary knowledge. The second most common reason for a smoking car battery is the fact that many people tend to charge their batteries after their car has been sitting for a while. Without even realizing it, a car battery can easily get overcharged causing the cells inside the battery to release the surcharge pressure in a form of highly toxic and even flammable smoke. A battery that has been overcharged is oftentimes completely ruined.

If you need to charge your battery, make sure you consult a professional before buying a battery charger and actually charging a car battery. Standard battery chargers are what most people used to have, still have today and can even be bought today as the cheapest option. These standard battery chargers only do one thing; pump the current into your battery until you plug them off. They have no way of knowing when the battery is sufficiently charged. Newer, smarter battery chargers that also cost more feature a processor that is able to recognize when a 40Ah charger fully charges a 40Ah car battery. When they reach that limit, they stop the current from coming into the car battery and shut off.

Internal short-circuiting

Although internal short-circuiting is rare in modern car batteries, it still can happen. If an internal short-circuiting happens the battery is discharged in a matter of minutes and as that happens a high current flow will cause the battery to heat and smoke. If and when that happens, there is absolutely nothing you can do. Modern car batteries also cannot be repaired after they short circuit so you will need to buy a new one.

car battery smoking

Loose battery connections

There is a reason why all the mechanics and battery replacement guides always point out the importance of really fixating the negative and positive terminal cables of the battery. If you fail to do so it might lead to complete failure of the battery due to a short circuit if the positive and negative cables somehow come into contact. 

Malfunctioning alternator

If it wasn’t for the alternator, we would have to charge our car batteries almost daily, like we do with our smartphones. Thanks to the alternator, the car battery is being charged as you drive. But just like all the components an alternator can fail in many ways. And one of those ways includes overcharging the battery to the point where it starts to smoke. A normal voltage of an alternator is between 13-15V which can be measured by your mechanic to determine whether it is your alternator that caused the battery to go bad. If this happens while you are driving, there is not much you can do, open the battery compartment and step away and wait for road assistance. Make sure you are not inhaling the toxic fumes coming out of the alternator.

Dead battery

In the last place, a battery that is way past its prime and what we would call “dead” is something that can also leak, smoke and smolder. If the battery is older than you can remember it is time to let it go. No amount of charging, or refurbishing is going to save it. Wait until it is safe to replace it and get a new battery. You might still be able to jump a car with an almost dead battery but we definitely do not recommend it. 

Is A Smoking Car Battery Dangerous?

Yes, it most certainly is! If the battery is smoking, smoldering or releasing fumes under immense pressure then you should do nothing but stay away and wait for it to cool off and calm down. A smoking battery releases toxic fumes and it represents a major fire hazard. 

Once it is safe to go near the battery, you can unplug it and remove it from your car. If  you are not sure when it is safe, call a professional. Never risk your well-being.

Are The Fumes And Smoke Coming Out Of The Battery Dangerous?

Yes, the fumes contain big amounts of chemicals, acid, and heavy metals which not only makes it dangerous to inhale but also a major fire hazard. Inhaling these fumes or smoke can lead to serious health issues. You must also stay away in case a fire or an explosion of the battery breaks out.

How To Prevent A Battery From Overheating And Smoking?

  1. Make sure you regularly inspect the state of your car’s battery. Inspect it for signs of leaks and swelling on the sides. Remember and write down when the battery was last replaced.
  2. Use the right battery for your car and environment. If you live in an area with extreme temperatures, make sure that the battery is suited for such an environment or that it is properly isolated and protected from the heat.
  3. If the battery does overheat, make sure a professional diagnosis is carried out. Find out why the battery overheated and solve the problem. Replace the battery if needed.
  4. Make sure the battery terminals are properly fitted and attached. Make sure that the ventilation tube of the battery is attached and functioning.
car battery jumper cables

Can You Drive With A Smoking Battery?

In theory, yes you can for a small amount of time. But in reality, if you see smoke coming from the battery compartment you should stop as soon as possible and wait for assistance. There is both a fire and a health hazard when driving with a smoking battery.

How To Fix A Smoking Car Battery?

In most cases, there is no way of fixing a smoking battery. If there was just a single occurrence of overheating, the battery might still be ok, but in most cases, once a battery releases fumes and smoke it is the end of that battery.

Buy a new battery on Amazon.com today (they have the best prices and you can easily find the right battery for your car by filtering the results for your exact make and model of the car)!


Seeing smoke coming out of your battery compartment can be shocking, especially when it happens for the first time and you might not even be aware that it can happen. If you own a new car or if you are a novice driver, make sure you learn where your car’s battery is located and how to inspect the state of the battery. By learning those two things you can both prevent the battery from ever starting to smoke, smolder and you can know from where the smoke is coming and how to access the battery compartment to let the fumes air out and the battery cool off. Make sure you check out our other automotive guides and how to’s.

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