What causes the battery warning light to come on?

Batteries

What To Do When Dashboard Battery Light Comes On

• Jan 21,2019

What Does the Battery Light Mean?

If your car battery light comes on when you start the car, you're in the clear! It’s completely normal for this light to illuminate when you first turn on your car. The light will turn off after a few seconds.

If the light stays on as you’re driving, though, pay attention. You'll likely notice other signs of a weak battery charge, like power windows that are slow to come up or a stereo that won't turn on.

An illuminated battery light could be due to a number of issues, including:

• A loose or corroded battery cable
• A problem with the alternator or voltage regulator
• Damaged cells or plates inside the battery
• Faulty wiring in the car's electric charging system

A dashboard battery light basically means there's a battery charging problem. Your car isn't getting enough voltage from the car battery to operate properly. It needs more "juice!"

Troubleshooting Your Battery Light

Now let's talk about your car battery light! It could mean it's time to replace the battery. But, the light could also be triggered by a minor (and easily fixable) issue like corrosion or loose clamps. So put on some protective gloves, consult your owner's manual, and then carefully follow the steps below to troubleshoot the battery yourself.

• Check for corrosion. In some vehicles, fumes from regular operation can cause corrosion to accumulate on top of the battery terminals, especially during summer months or in regions with year-round warm weather. To check for corrosion, remove any covers from the terminals on top of your battery. If you see a white or greenish substance on the top of the battery or around the terminals, you've got corrosion! While battery corrosion is common, it can interfere with the conduction of electricity from the battery to the rest of your car. Don't touch battery corrosion with your bare hands, as it could cause skin irritation. Instead, head to our next troubleshooting tip.
• Clean the battery terminals. If you noticed significant corrosion or other grime around your battery terminals, this could be why your car battery light is on. Fortunately, it’s easy and inexpensive to clean your battery terminals with common household items and a bit of elbow grease. Simply remove the terminal covers, disconnect the battery cables, and give the terminals a hearty scrub.
• Tighten the cable clamps. Sometimes a car battery light comes on because there's a weak connection between your battery and the cables that connect to it. While you have the hood open, check to be sure the clamps are securely fastened to your battery terminals. If you notice that the clamps are loose, use a small wrench or a pair of pliers to tighten them until they’re snug around the terminals. Consult your owner's manual for specific instructions related to your vehicle make/model.

What to Do When Your Car Battery Light Is (Still) On

You've checked for and cleaned off any corrosion, and you've tightened up any loose battery cables. But your battery light is still on?! The culprit could be a mechanical issue, like a problem with the alternator or voltage regulator. Or, it could be something systematic, like faulty wiring.

What’s next? Head to Firestone Complete Auto Care for a fast and free battery check. We’ll take a look at your battery’s health, then recommend repairs or a new battery if needed. Don’t get stranded because of battery issues! Find your nearest Firestone Complete Auto Care today and recharge your peace of mind.

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That battery light staying on isn't necessarily a sign that you need to get a new battery. Bjoern Wylezich/Shutterstock

Every gasoline-powered or hybrid car today contains a rechargeable 12-volt battery. This battery powers everything electrical: the engine's control computer, the ignition system, the radio, the headlights, etc. So, the battery is vital to the car's operation.

Like all batteries, a car's 12-volt battery would eventually go dead if it were not recharged, so your car has a built-in recharging system. The alternator and voltage regulator charge the battery and provide electricity to the vehicle when the engine is running. A typical alternator can put out between 500 and 1,000 watts when necessary.

Because your car is so dependent on the battery, any car with a combustion engine and a 12-volt battery has a light on the dashboard that warns you if the recharging system fails. It looks like a little battery, or sometimes it says "Battery." A simple circuit looks at the voltage that the alternator is producing and turns the battery light on if that voltage is low. So, the light is telling you "your alternator is not properly charging." It's not telling you "your battery is bad or needs to be replaced immediately." You don't have enough information yet.

The battery light comes on when you start your car, and it might linger for a second or two, but it usually turns off pretty quickly. If it stays on while the car is running, it probably means there's something wrong with the alternator. It could also mean there is a minor problem with the battery like corrosion. Either way, it's something you want to check out.

If there was enough juice for you to start the car, then you can safely drive the car on however much charge is remaining, but it won't last long — maybe 30 to 60 minutes max. If the battery isn't being charged, the electrical systems will start to fail.

Use whatever charge is remaining in the battery to get somewhere safe, either an auto repair shop or your home. Once you turn the engine off, it might not come back on again. To eke out every minute of charge, turn off as many electronics as you can: radio, air conditioning, heated seats, even the headlights if it's daytime. Unplug your phone too, since every little volt counts.

Originally Published: Apr 1, 2000

Battery Light FAQ

What does the battery light on a car dashboard mean?

The battery light on your car dashboard signals a charging problem with your car battery. If the light turns and stays on, it might be that your alternator isn’t generating enough voltage to charge it. Common causes can be a broken alternator belt, damaged battery cells or a failed alternator.

How long can I drive my car with the battery light on?

If your battery light stays on while you drive, you’ll have roughly 30-60 minutes to drive with your battery lights on before your car may start stalling.

How do you tell if it's a dead battery or bad alternator?

If you vehicle has a dead battery, it may not start or may have difficulty starting, have dimmed or flicking lights or an issue with the sound system. If it stalls while you’re driving or your engine turns off suddenly, the alternator is malfunctioning or not recharging your battery.

How do I fix the battery light on my dashboard?

Try turning off all the lights and other systems that can drain your battery. If the problem persists, stop the vehicle and let it cool for a while. If it still doesn’t work, drive straight to your mechanic to have them take a look.

Why does my car operate with the battery light on?

If your battery lights stays on and your car seems to operate normally, you need to head to a mechanic. Your vehicle is draining the energy left in the battery and it will die fairly soon.