It goes without saying that smoke from under the hood doesn’t always come from the battery. As a matter of fact it usually doesn’t. Hot manifolds can produce smoke due to dripping fluids, contact with rubber or wiring, etc. Overloaded electrical wiring can produce a lot of smoke very rapidly.
Leaky cooling systems (hoses, radiators, etc.) can produce steam. Blocked airflow or an inoperative cooling fan can in some cases cause the A/C compressor pop-off valve to release refrigerant.
In some cases, the battery can also emit smoke.
Here are some of the frequently asked questions (FAQs) from drivers who want to know more about their car battery and why it could emit smoke.
A smoking car battery can mean many things. Below are the most common ones.
This kind of battery smoke is typically caused when the battery is connected to a charger that is set on a high charge rate for too long. Higher end chargers will have high charge settings (40 to 60 amps) and a timer, but these chargers will also have lower charge settings. An inexpensive charger will typically only have a 2 and a 10 amp setting.
When charging a battery for a long period of time (longer than a few minutes), always use lower rates of charge to prevent the battery from overheating.
The acid electrolyte tends to bubble a bit during normal charging due to the heating of the plates in the battery and the escaping gas stinks and is explosive. Keep sparks and flames away from the area and never connect both jumper cables clamps directly to the battery. Always connect the ground cable last, and connect it to a heavy metal spot on the engine.
When charging a battery for a long period of time (longer than a few minutes), always use lower rates of charge to prevent the battery from overheating.
– Richard McCuistian, ASE Certified Master Automobile Technician
In extreme cases, a battery can explode if it is charged aggressively for long enough to boil the electrolyte out of the battery. Battery explosions are loud, sudden, and dangerous, throwing whirling shards of sharp plastic in several directions.
If you are charging a battery with a heavy duty charger, watch the battery voltage carefully. If the charging voltage goes higher than 15.5 volts after 3 minutes or less, the battery is sulfated. The plates are coated with sulfur, and the battery should be replaced. Typically, the only reason for a high amperage charge is to get a vehicle started that has totally killed the battery. Otherwise, use lower charge rates (10 amp or less).
Important note: Whenever you’re working around a lead-acid car battery, always wear eye protection.
The alternator keeps the battery charged as you drive by using the principle of electromagnetic induction to generate electrical power from mechanical power.
The alternator is designed to produce an electrical pressure higher than the battery voltage to charge the battery.
Voltage is like electrical pressure, you see. And too much pressure is damaging to the battery.
The voltage regulation system (either stand-alone or built into the PCM) controls the magnetic force created by the spinning rotor in the alternator, and that magnetic field creates alternating current in the stationary windings of the alternator (the stator). That voltage is fed through a rectifier bridge, converting it to DC current, which charges the battery.
The voltage regulation system (regulator or PCM) measures battery voltage and alters the strength of the magnetic field in the rotor to control charging. If the regulation system malfunctions, it can overcharge the battery, causing all the same problems previously described, only it’ll happen while you’re driving rather than with the hood open and a charger connected.
It gets awfully hot under the hood. That’s why most vehicles have a plastic box or cover over or around the battery to keep it cooler than it would be without it. Don’t discard the plastic box if you’re replacing the battery. If the plastic cover is missing, see about getting a replacement. When the battery runs too hot, the electrolyte can steam out of the battery and chalk up the battery terminals, rust the battery box, etc.
An internal short-circuit can discharge the battery and produce a high current flow that can cause the battery to heat up and produce smoke. This rarely happens with modern car batteries, but once it does, damage is irreversible, so you might need to buy a new battery.
This can happen without warning. If you see your battery boiling when the car is parked and the hood is open, be very careful, protect your eyes, and get something done about it immediately.
A car that’s been sitting for a long time will probably have an old battery as well. In some cases, jump-starting an old battery can cause it to smoke, smolder, and leak fumes.
Note that a totally dead battery that is disconnected from the vehicle can be charged backwards if the person using the charger connects it that way. Connecting a backwards-charged battery to a modern vehicle can ruin all sorts of expensive parts.
Yes. Not only is a smoking car battery a fire hazard, but it can have adverse effects on your health, too.
Vented battery gases contain toxic fumes called sulfuric acid. If a person is exposed to this chemical, he or she is at risk of experiencing skin and eye irritation, and respiratory and gastrointestinal problems.
So if you ever find yourself accidentally exposed to a smoking car battery, immediately call for help and seek medical attention.
There’s no good way to fix a battery, but just because a battery is smoking doesn’t mean it’s necessarily bad. There might be some instances where the battery will work fine after a short period of overheating, but for the most part, you’ll need to buy a new one instead.
A new battery can cost anywhere between $200 and $500, depending on several factors. Some of these include the brand, and your vehicle’s year, make, and model.
Learning how your battery works can help you keep it working for a long time with no issues.
Automotive batteries can last anywhere between three and seven years.
Battery capacity is determined by the amount of active plate material in the battery. If the battery has a lot of thin plates, it can produce high currents for a short period of time.
Meanwhile, a few thick plates will make the battery produce a low current for a long period of time.
Batteries used in newer models usually feature a maintenance-free design. This design features lead-calcium instead of a lead-antimony plate grid construction, which consumes less water during battery service.
Compared to lead-calcium, lead-antimony batteries produce less gas, which means the battery terminals, wiring, and support trays won’t corrode as much.
Cleaning the battery terminals is essential to keeping the battery in tip-top shape. In most cases, corroded battery connections lead to electrical faults.
Fortunately, this kind of problem can be resolved at home. Baking soda mixed with water can help neutralize the acid on the connections. From there, you can wash the area regularly with water.
Checking the battery hold-downs is also another maintenance task you shouldn’t skip out on. Make sure that the battery is secured with sturdy brackets to prevent it from moving around as you drive.
It might be time to replace or recharge your vehicle’s battery once the following symptoms are present:
Reduced battery capacity won’t be able to supply the necessary current to start the engine.
Too much corrosion on the battery cables or connections could mean that the battery is sulfated. A sulfated battery can release acid fumes and travel through the vent holes, affecting the cables, connections, and tray.
Water in one or more cells is also a sign that the battery plates are sulfated. This symptom also means that the water in the battery’s electrolyte is being separated into hydrogen and oxygen gases.
Similar to other engine components, the battery can also heat up and emit smoke from under the hood. Excessive heat, overcharging, and an internal short-circuit are some of the most common causes of this problem.
A smoking car battery is both a fire and safety hazard, which is why it’s essential to call for help and seek medical attention when exposed to its fumes.
Lastly, a smoking car battery usually means irreversible damage, so might as well get a new one if you ever find yourself dealing with this kind of issue.
Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic. The accuracy and timeliness of the information may change from the time of publication.