Why Is My Car Battery Smoking?

Your car battery is a compulsory component of your car for it to function at all. Keeping your battery in proper condition is essential to supply the vehicle’s engine with the necessary power to work.

It is unusual to encounter problems with your car battery, such as alternator issues, corrosion, inability to hold a charge, and deep discharge. The focus of this article is smoking. The fumes released from this issue are usually smelly and toxic. 

What Causes a Car Battery To Smoke? 

Different reasons are culpable for a car battery’s smoking. The most likely ones are; 

  • High temperature
  • Overcharging
  • Faulty alternator 
  • Poor connection
  • Damaged battery 
an old car battery

High Temperature

In most high-temperature environments, overheating is very common due to the heat. This mostly happens in tropical environments or during summertime. Overheating causes the electrolyte to heat up and evaporate, producing smoke. 

How to fix/control overheating: some battery makes resistant to damage by heat. The insulation prevents the electrolyte from boiling over. Investments in batteries with a durable casing are recommended to protect from heat. 


It is certainly advised that you monitor your battery while it charges and disconnects it from the charger once full. The effects of overcharging include reducing the battery’s life span, lowering its efficiency, and causing the electrolyte to boil, which swells up the casing. Gassing happens when the electrolyte heats up and generates hydrogen and oxygen gas. This gas is toxic and highly flammable. Gassing could open the battery in sealed batteries, which is very dangerous. For older vented batteries, the electrolytes evaporate and expose the plates. 

Some chargers are made to stop when the battery is fully charged automatically. Also, float or maintenance chargers like Battery Tender keep the battery charging without damaging it. However, monitoring the charge levels is the safer bet. 

Faulty Alternator

An alternator is responsible for recharging a car battery while it is in use. It converts chemical energy to electrical energy to replenish the battery’s charge and power the electrical parts. Alternators go bad sometimes due to wear and tear, heat from friction, and accumulation of dirt. A damaged alternator is a common cause of smoking in marine batteries- it causes overcharging, which is also a reason for battery overheating. A normal alternator should have a voltage of 13.7 to 14.7 volts. It is best to let a technician fix the alternator issue. 

Poor Connections 

Loose connections at the battery terminals can lead to internal shorting, which harms the car battery. Ensure your terminals are properly tightened to prevent shorting. Also, contact between the positive and negative plates can lead to shorting, causing the battery to gas heavily. 

Old Battery

Your car battery could be smoking because it is old and worn out. If this is the case, you should start looking to get it replaced. Car batteries last for up to four years or more if well handled.

How To Handle A Smoking Battery  

If your battery starts smoking while driving, the first thing to do is pull over and follow the steps below;

  • Put on safety gloves.
  • Place a fire bucket or pan under to place the battery in case it catches fire. 
  • Disconnect all power sources; turn off the ignition, remove the keys and turn off any lights. Also, open the door and windows. 
  • Take out the battery for testing by a technician and find an alternative to keep moving. 

Why Does the Smoke Smell Bad?

The rotten egg smell comes from the reaction of sulfate and damp air. An automotive lead-acid electrolyte is made of sulfuric acid and water. Higher temperature makes the mixture evaporate, releasing gasses that can be smelly. 

The likely culprit of the smell is called thermal runaway. Thermal runaway is when the chemical reaction in the battery goes beyond control and produces a lot of heat. It is dangerous and can lead to fire, which burns the battery component to melt and produce a bad plastic smell. Another cause is a power surge which happens when you jump-start the battery with another faulty battery or connect the cables to the wrong terminals. This can lead to acid leakage, causing smoke and smelly fumes. 

Is A Smoking Battery Dangerous? 

A smoking battery is a fire hazard and should be treated urgently. The released gas is toxic, choking and poisoning the system when inhaled. The dangerous chemicals released, such as hydrogen fluoride HF, phosphorus pentafluoride (PF5), and phosphoryl fluoride (POF3). are not safe for the human body, leading to respiratory problems and, in extreme cases, death. It is best to allow a professional to diagnose and fix the smoking battery because it is not safe. 

Proper Maintenance of A Car Battery 

To extend your car’s battery life, here are a few tips you should take;

Control Corrosion 

Batteries are prone to rust around the battery terminals due to contact with moisture and electrolyte gasses. A way to control corrosion is by coating the terminals with petroleum jelly, anti-corrosion spray, or using anti-corrosion washers. 

Avoid Taking Frequent Short Rides 

Your car battery charges as it moves, so taking short rides charges it for a short time, not fully. Avoid too many consecutively short rides to preserve your battery’s lifespan or keep a portable car changer handy when stranded. 

Check The Battery Regularly 

As simple as it sounds, a simple casual inspection of your battery regularly increases its lifespan and prevents damage. It helps you quickly detect defects and fix them before they go out of hand. You can take your inspection up a notch by checking the voltage from time to time with a voltmeter or multimeter set to measure voltage. Use the device’s probes to touch the respective terminals of the battery and observe the readings. Anything below 12.4 volts means your battery is weak and needs to be disposed of for a new one. 

Final Thoughts

Car battery smoking or overheating is rampant during the summer, so extra caution and care should be taken. However, it can happen anytime and at any period. Avoid trying to manage the battery. If you notice it smoking, call a technician immediately to diagnose and fix it. 

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