7 Causes of a Car Battery Light On While Driving

There are a variety of reasons which can cause the battery light in the car to illuminate while driving. Below are the top 7 reasons to help you diagnose the problem. Sometimes you may experience more than one of these reasons, but this list will give you a rough idea of what to look for in your vehicle.

Once you figure out the cause(s), you can work to correct the problem. This could mean fixing certain components or replacing entire components or parts.

Corrosion at Battery Terminals

This is a common problem and usually lets itself known by making your vehicle difficult to start as the starter motor turns over slowly. But sometimes corrosion on the battery posts or terminals can interrupt the flow of electricity and not allow the alternator to do its job. This will cause the battery light to stay on after you start your vehicle.

If you notice a white-ish crusty or powdery substance where the battery cables meet at the posts, you have corrosion. The fix is easy. Simply disconnect the battery cables and then use a mixture of baking soda and water (1 Tbs added to 200 ml of water) to clean the ports and terminals using a toothbrush. Alternatively, you can use a battery terminal cleaner brush or wire brush to remove the corrosion.

Loose Car Battery Cable

The same way a corroded battery terminal causes an incomplete charging connection, a battery cable that’s simply not connected tight enough can cause the battery light to come on while driving. Often this happens immediately after hitting a bump in the road or after installing a new battery.

To fix, make sure the battery cable terminal is seated as far down on the battery post as possible and then simply take a wrench or socket (10mm for most vehicles) and tighten the nut on each terminal until it stops turning. If you notice some corrosion as well, make sure to clean that off before tightening.

Weak Battery

If your battery is over 3 years old, don’t assume the battery itself is not at fault or even completely dead. This is especially true if you drive your vehicle frequently every day or live in a hot geographical region, like Florida. Car batteries tend to die a lot faster when they’re used in hot temperatures. If your car battery is on the verge of death, it will cause your car light to come on at any time.

Even though car batteries are sold as having warranties at different lengths (ie: 48, 72, or even 96 months), don’t expect them to last that long… they rarely do. Depending on when a battery fails during its warranty period, you may be entitled to a free replacement or a pro-rated credit toward a new battery.

To confirm a bad battery, use a multimeter to test its voltage. Connect the negative lead to the negative battery terminal and positive (red) lead to the positive battery terminal. You should get a voltage reading somewhere in the vicinity of 12.4 and 12.7 volts. If the reading is lower than 12.2 volts, you may have a battery that needs replacing.

Bad Alternator

Alternators typically last about 5 to 7 years (roughly 80,000 to 120,000 miles) in a vehicle. As you know, the alternator is responsible for keeping the battery fully charged as you are driving the vehicle. But if you have a bad alternator, then it won’t be able to keep the battery charged.

This will cause the car battery light to illuminate once there is an inconsistency in the charge. Once the alternator completely dies, the power that is left in the battery will be exhausted in a matter of minutes. If you have a faulty alternator, you will either need to replace it or have it rebuilt.

Bad Alternator Belt

The alternator belt is what connects the crankshaft and alternator together. If you have a bad, loose, or torn alternator belt, then your alternator won’t be able to function properly. As a result, your car battery won’t receive the charge it needs to power your vehicle’s electrical components. So, your car battery light will come on because of this.

Replacing the alternator belt with a new one is the only option.

Bad Ground Strap

The ground wire of your vehicle connects to the negative terminal of your car battery. If the negative battery cable ever becomes excessively damaged or worn out, it will affect the flow of power to the electrical components of your vehicle. Furthermore, the bad ground wire can cause the battery light to come on as you are driving.

If you see any damage to the ground wire, you will need to replace it.

Too Many Accessories

If your battery has the proper voltage and your alternator is recharging it as it should, the number of accessories you have turned on while driving shouldn’t cause the battery light to come on. But, if the charging system is not working optimally, the number of electrical components in use while driving can drain the battery at accelerated rates.

Your car’s heating, air conditioning, power steering, and headlights require a lot of power. Once you start adding in other accessories like windshield wipers, stereo, rear defroster, fuel pump, GPS system, DVD player, or even charging your cell phone, the electrical requirements start to add up.

If you notice your battery light turn on while driving, try turning off the A/C or any other non-essential components to see if that helps. At the least, you’ll preserve the amount of stored energy in the battery to allow you to get to your destination and then fixing the issue.