Picture this: it’s dark outside, and you’re driving home after a long day at work. Your headlights begin to get dimmer and dimmer before suddenly, your entire vehicle turns off.
You try to restart the vehicle, but your battery is completely dead. What happened? Why did it happen? Could this have been avoided?
A car’s battery can completely lose all of its charge while driving. In this article, I’ll explain why, how to prevent it, and what to do if this scenario happens to you.
Can a Car Battery Die While Driving?
Your vehicle’s battery can die while you are driving. This can happen for a number of different reasons, but the root cause is the failure of the vehicle’s charging system.
A vehicle requires electricity to power accessories like lights, the radio, and the fans for the interior heating and cooling system. Even the most basic automobile also requires electricity to run the engine, from turning the starter to start the engine down to providing power to the spark plugs to ignite the fuel that powers the engine.
Modern vehicles with more complicated systems have even more components that require electricity, like computers that control the engine’s parameters when the automatic transmission shifts and even electronically controlled suspension in the most high-end vehicles.
In order to power all of this, a car has a 12-volt battery. Like a cell phone, electronic toy, or a flashlight, this battery discharges with use.
In order to make up for this lost energy, vehicles have an electrical charging system to actively recharge the battery while the engine is running.
When this charging system cannot provide as much energy as the car is using, the electrical system works at a net loss, meaning that the battery is slowly discharging until the battery finally dies and the vehicle loses all power.
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This can happen when the vehicle is being driven, presenting a dangerous situation, particularly at night. Without electricity, the vehicle’s headlights and taillights cannot function, making it difficult for the driver to see the road ahead, and limits visibility to surrounding vehicles.
As the engine requires electricity to run, the engine will also stop running when the battery dies. This also presents a danger, as many modern vehicles have power steering that has a pump run by the engine and power brakes that are assisted by the vacuum produced by the engine.
As a result, when the engine dies as the result of a battery failure, steering and braking become significantly harder.
In rare situations, battery failure can also be caused by an overactive charging system, causing the battery to explode under the hood!
No matter how your vehicle’s electrical system fails, it is hardly an ideal situation!
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How Does a Vehicle Charge its Battery?
Automobiles have an electrical charging system to charge the battery as the engine runs and prevent the battery from discharging completely. This charging system uses some of the mechanical power produced by the gas or diesel-powered engine to generate electrical current with an alternator.
An alternator is a small automotive generator that converts mechanical energy from the engine to electrical power in the form of alternating current.
The engine transmits mechanical energy to the alternator via a pulley and belt run from the engine’s crankshaft, just like an engine’s water pump, air conditioning compressor, or power steering pump.
The alternator consists of a metal rotor and an armature made up of windings of copper wire that produce a spinning magnetic field. As it spins, this magnetic field produces alternating electrical current.
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A car battery, however, must discharge and be charged by direct current (DC). So the alternating current (AC) that the alternator produces must be directed to a regulator and rectifier that converts alternating current to direct current and then limits the voltage provided to the battery so as not to overload the battery.
As a result, as the engine runs, alternating current is produced, converted to direct current, and recharges the battery. As long as the alternator can produce as much electrical power as the vehicle uses, the battery remains charged.
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How Can a Battery Fail While Driving?
A battery can fail while driving because of an alternator that contains rotating components that rely on bearings to spin smoothly. These bearings can fail due to damage, overheating, or just simple wear over time, and the alternator stops charging the car battery.
As the bearings fail, the alternator becomes less and less efficient, as more of the mechanical energy provided by the engine to the alternator is lost as heat because of the bad bearings. A less efficient alternator will often not be able to produce enough electrical power to properly charge the battery, and the battery will die over time.
Corrosion of the alternator can also cause charging system problems, as corrosion on the copper windings will also reduce the efficiency of the alternator. Liquids spilled on the alternator can also interrupt the magnetic field, stopping production of electricity.
A failed rectifier will also keep a battery from charging, as there is not the direct current the battery needs to charge.
A failed voltage regulator has the opposite effect, as unrestricted voltage is fed to the battery, overloading the battery. At minimum, this causes the battery to die. Worst case, however, this can cause the battery to explode and other components on the vehicle’s circuits to overload and fail as well.
A 12-volt battery should only be charged by a 12-volt source!
Does Idling Cause a Battery to Die?
Idling can’t cause a car better to die. Your vehicle’s charging system should produce enough electrical power to maintain the battery when idling.
If your charging system is compromised by a faulty component, however, it may not produce enough energy to keep the battery charged.
The alternator may not be working at peak efficiency and may not produce enough power to charge the battery at low RPM while idling.
A faulty regulator, rectifier, or defective battery can cause battery failure regardless of whether or not the vehicle is just idling or driving.
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What Should You Do if Your Car’s Battery Dies While Driving?
When your car’s battery dies while driving, you should assess the surroundings, avoid panic, prepare for more difficult steering and breaking, safely pull over and call for help.
Electrical failure can result in a very dangerous situation depending on the circumstances involved.
The first important point is to remain calm and do not panic. This will allow the driver to better assess the situation and make the best decisions on how to safely bring the car to a stop on the side of the road.
Next, the driver should assess the surroundings. Is the vehicle traveling uphill, downhill, or on flat ground? How much traffic is around? Where is the nearest safe place to pull over?
If the vehicle is traveling uphill, the driver needs to find a safe place to pull over more quickly, as the vehicle will not travel as far without power uphill. If the vehicle is traveling downhill, the driver has more time to find a place to pull over before the vehicle stops moving, but must be very careful with brake management.
If the vehicle is equipped with power steering and power brakes, this power assistance will cease once the battery dies and the engine loses power.
The driver needs to be prepared for more difficult steering and reduced braking performance. If the brakes are too weak without the vacuum power assistance from the engine, the driver needs to use the handbrake or emergency brake to safely come to a stop. The driver should engage the handbrake gradually so as not to lock up the tires and lose control.
The driver’s main goal should be to safely pull over.
If it is dark out, the driver should use extra caution due to the reduced visibility of the road ahead as well as the reduced visibility of the vehicle to surrounding drivers. Once the vehicle is pulled over, the driver should use some other light (flashlight, cell phone, glow stick, etc.) to increase visibility to passing drivers.
In the end, you should call for help. Make sure someone you’re calling to or you have jumper cables to be able to charge your car’s battery. Alternatively, you can pull over other road users to help you.
When your car battery is charged, drive immediately home or to the mechanic because your car battery will die soon again.
Battery failure while driving can be a dangerous experience, but with the right mindset, these risks can be greatly reduced!
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How to Prevent Battery Failure while Driving?
Battery failure is never 100% avoidable, but there are actions a vehicle owner can take to reduce the risk.
If you want to prevent car battery failure while driving, regularly inspect (or have a mechanic inspect) the alternator for any corrosion, liquids leaking onto it, or any odd growling, squeaking, or clicking noises that would suggest bearing failure.
Most cars have a gauge on the dash that indicates charging performance. The needle should read at or near the center of the gauge under most conditions. The needle may rise a bit above center for a short while after the vehicle is started. This is completely normal as the vehicle must charge a bit after the battery has been sitting.
If the gauge reads below center or very high above center, this is a sign of charging system failure, and the vehicle should be diagnosed and repaired promptly to avoid battery failure while driving.
If you pay attention to the warning signs, dangerous situations due to battery failure while driving can be avoided!