If you’re driving along and the automotive battery warning light appears, there’s no need to panic.
This guide will explain what you should do and the mechanics of what might be going wrong.
Every modern car – including yours – will have a 12-volt battery and circuit, charged and powered by an alternator. Each time you start your engine, all the dashboard lights should illuminate and vanish, including the car battery warning light.
When a car battery warning light appears on your dashboard while driving, it means the electrical systems in your vehicle aren’t receiving sufficient power.
This guide will explain how a car’s battery and electrical system operate and go through some potential causes of the warning light coming on while driving.
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Table of ContentsShow
What Is A Car Battery?
Car batteries work in precisely the same way as other commercially available batteries. Through a chemical reaction, they supply electrical power to a circuit.
A car battery’s primary responsibility is to drive the starter motor, which gets your engine running when you turn the key in the vehicle ignition. Without it, we’d all still be hand-cranking our massive engines!
Once the engine is powering itself, the alternator takes charge of running most electrical components in your vehicle, with some battery assistance. This includes lights, spark plugs, radio, heater, windshield wipers, etc.
When you’re driving, the alternator is responsible for recharging. For this reason, a working car’s battery has a greater output voltage than a stationary one. The auxiliary drive belt powers the alternator.
It takes about 30 minutes of freeway driving to recharge a battery completely. In a city, it could take around an hour. That’s why making multiple short journeys is damaging for your car’s battery (and other systems, too).
What’s The Voltage Of A Car Battery?
All standard cars come with 12-volt batteries and circuits, including the component circuitry in electric vehicles. Previous models might come with a 6-volt version.
With the engine off, connecting a voltmeter across the terminals of a completely charged battery should give you a reading of 12.6V (although 12.5V is low but acceptable). When the engine runs, the output should be roughly 14V (between 13.5V and 14.5V).
The battery comprises six 2.1-volt cells, which the observant amongst you will note adds up to 12.6 Volts rather than 12. The “12-volt” class is a nominal, standard term for this kind of lead-acid battery, stemming from the days of 6-volt batteries.
The older 6-volt batteries had three 2.1-volt cells, producing 6.3 Volts. This number was then rounded down to 6.
The newer, more durable batteries had six of the same cells, making them twice as powerful. Thus, we call them 12-volt batteries, even though it’s tempting to round their output up to 13 Volts.
Why Can I See A Battery Light While Driving?
If the battery light comes on while driving, the car’s ECU (basically, its brain) has registered that the electrical system isn’t putting out sufficient volts to run the vehicle correctly.
Sometimes, your battery or alternator may go through a temporary blip where it momentarily throws out a less-than-expected voltage. This could be an initial sign of a possible problem.
If you have a constant battery light on while driving, there’s either a problem with the battery, the alternator, or a loose connection somewhere.
Symptoms Of A Struggling Electrical System
If the battery light comes on, you may also notice some of the following telling symptoms:
- Poor performance from electrical systems (such as dim headlights, interior lights, dashboard lights, windshield wipers, etc.).
- Poor engine performance could stem from a low-quality power supply to the spark plugs and fuel pump (and possibly injectors).
- Losing electric power steering, which is particularly dangerous. Immediately pull over in this situation.
- Rough idle or stalling at idle.
- Trouble starting the car when you get in, and possibly even a dead battery.
- Whining noises – probably caused by a damaged or detaching alternator pulley.
Of course, these are all rather crucial issues and could be hazardous in the wrong circumstances. It’s vital to find and fix the problem as soon as possible.
What Causes The Battery Light To Come On While Driving?
If the battery light comes on while driving, remember: it’s not necessarily an issue with the battery!
The caution light means the electrical system isn’t getting sufficient power. This could stem from a few different places – the battery, the alternator, or the wiring connecting the parts and elements.
Battery Can’t Hold Charge
You’ll know a battery can’t hold a charge if it struggles (or fails) to start or crank when you turn the key. The alternator might be operating fine, but if it’s trying to recharge a defective battery, the ECU will recognize and trigger the light.
Of course, batteries are perishable components. They won’t run forever, just like how your smartphone’s battery life is finite and shorter with every charge.
A dependable battery typically lasts around three to five years, but seldom longer. When a battery malfunctions, it is usually due to one of these reasons:
- Damaged cells.
- Broken plates.
- Leaking battery acid.
These would all hinder the charging and discharging processes, causing the device lamp to come on.
Use a voltmeter or battery tester to check its condition, both with the engine off and running. You should see 12.6 Volts and about 13.8 to 14.2 Volts, respectively – any lower could indicate a defective battery.
Simply exchange it out for a fresh one. It shouldn’t be too costly.
Poor Alternator Output
An alternator is an electromagnetic generator driven by the auxiliary drive belt (the belt you can see on the lateral of your engine under the hood). It generates alternating current (AC) and passes through the rectifier, transforming it to DC (direct current) before passing through the electrical regulator.
The regulator should ensure that the alternator always delivers between 13.5 and 14.5 Volts to the car’s circuit. It simply switches its output off whenever it’s unnecessary.
If the alternator isn’t operating correctly, it won’t put out enough Volts and, therefore, can’t fully power components or recharge the battery.
Should the alternator stop working entirely, the electrical system will draw all its power from the battery, giving you a total of 30 minutes before it completely discharges and the engine stalls.
These circumstances will cause the battery light to come on while operating.
You can test an alternator by using a portable battery tester. These are broadly available and should come with options to check the condition of the battery, the alternator, and the starter motor.
If the test shows a poor alternator output, you’ll need a replacement part. Experienced mechanics may be able to take it apart and swap out the defective component, but for you, as a customer, this is generally the costlier option.
Bad Wiring, Terminals, Connections, Or Grounds
Unless a faulty wiring or connection problem is immediately apparent, you’ll probably need some professional diagnosis work from an automotive electrician to find it.
A car’s 12V circuit runs from the battery/alternator through wires to the various components. These devices are then connected to the vehicle’s chassis (“grounded”) to complete the circuit, returning the electrons to the battery.
If the battery’s terminals – the two knobs or “posts” sticking up, labeled “positive” and “negative” – are damaged or corroded, the voltage would also be impeded. Try reconnecting them to the wires and lubricating the terminals with a suitable grease.
The circuit can’t transfer sufficient electrical potential if there’s a problem with either the wiring or the grounds. As a result, you’ll get a cautionary light.
Of course, there are thousands of grounds and connections throughout a vehicle. As a result, expert diagnosis services might be necessary.
What Should I Do If The Battery Warning Light Comes On While Driving?
With the battery warning light on, aim to get somewhere safe nearby where repair work can be carried out, such as a nearby auto shop or your home’s driveway. Get off the road as soon as practically possible.
Once there, try restarting your engine to see if the light is still apparent. If so, it might be worth calling out your breakdown assistance company.
In the meantime, try not to switch the engine off until you reach your ultimate destination. If your car has a stop/start system, the ECU should automatically disable it – but it’s worth checking.
For the same reason, do your best to keep the engine revs relatively high, especially if you can feel the car struggling at idle. If you’re driving a vehicle with an automatic transmission, select a slightly lower gear than normal and try to avoid stopping. In manual cars, simply keep your foot on the gas pedal when you’re stopped.
Turn off additional things like the radio, fans, and heated parts to reduce the electrical load. Stay in the slow lane if your car isn’t running well. Use hazard lights if needed. Don’t turn off the headlights if it’s dark.
Conclusion
Sometimes, you’ll find that the battery warning light has disappeared when you next start your car. It might not reappear again for some time, which could also represent a developing problem.
If the light remains illuminated during several trips or turns on during the middle of your journey on consecutive days, there is a higher chance of experiencing a major electrical problem.
You may be able to find the issue yourself with some fundamental diagnostic tools like battery testers or standard voltmeters. However, if not, be prepared to take the car to a specialized automotive electrician.
The diagnosis might be rather expensive ($100 to $500, depending on the complexity). A new alternator might come to around $400, including labor. In contrast, you can expect to pay up to a little more than $100 for a new battery.
If the battery warning light comes on, repair it as soon as possible. Don’t try to ignore it – keep the road secure for you and everyone else.
