Car Battery Light On

The “car battery light on” problem is one that’s often misunderstood. In a perfect world, it would simply mean there's a problem with the battery, right? But of course it's not that simple. The car battery light is important, though, since it indicates a problem relating to the charging system. That means the problem could range anywhere from the connection between your battery and the car, the alternator belt, or to the alternator itself. We'll walk you through what the car battery light means and how to fix it

red battery light in car

How Your Car’s Electrical System Works

Your battery produces 12 volts - well, 12.6 V to be exact - which is used to start the vehicle and operate many electrical systems. However, the alternator is responsible for producing the electricity that keeps your battery fully charged while you drive. When your battery light comes on, it means that something is preventing the charging system from doing its job. One way to think of that battery light is that it’s a “battery not being charged” light. And, therefore, you should not count on being able to drive for too much longer when that light comes on. 

Fortunately, Advance Auto Parts stores offer a range of free services, including testing your battery, starter and alternator*. 


When the computer detects any problem with your car’s electric system, or with the recharging system in particular, then you’ll run into the “battery light on” issue. With cars being so dependent on their batteries functioning properly, a system is in place that measures the voltage produced by the alternator. If the voltage is not within certain parameters, the light goes on. Car batteries are designed to deliver powerful bursts of electricity to engage the starter, unlike other types such as the DieHard marine battery, which discharges more slowly. One common cause of the battery light is a loose or worn out serpentine belt. The other common problem is a bad alternator. Less commonly, there may be a problem in the wiring between the battery and the alternator or a different problem such as a loose battery cable connection.

can i drive with the red car BATTERY LIGHT ON?

With the red battery light on, you can drive, but not for too long. Typically, you might have about half an hour to drive on battery power alone. This can vary, though, according to the vehicle you drive and the health and charge of the battery.

If you notice the battery light on, go ahead and turn off unnecessary electronics, such as your stereo or even the A/C. This easy step can help you get a little farther down the road. As your battery discharges, you’ll also notice some loss of functionality, such as dim or flickering lights, and accessories like the radio or heated/cooled seats shutting down even if you haven't turned them off.

a man in a home garage looks at an alternator he's holding

How to fix the battery light

To recap some of what we’ve covered, here are the basic steps you can take to pinpoint the cause of your battery light.

  1. Start with what’s easy and quick by making sure your battery cables are secure and free of corrosion.
  2. Check the serpentine belt and replace it as needed. Since most vehicles use a serpentine belt to power accessories under the hood, be sure to check the tensioner for the belt, too, which can also fail and cause a loose belt. If your belt doesn’t make good contact with the alternator pulley, it can slip, causing your alternator not to produce full power. To fix this problem, the belt will usually need to be replaced. You can try tightening it first, though.
  3. Test the alternator output with a multimeter. Here’s a guide to doing this simple test.
  4. Replace the alternator if it’s found to be the problem. Keep in mind that many times the battery will have been drained past the point of being able to recharge and you may be replacing it soon, too. Here’s how to test your battery at home.

If there is no obvious problem, then we recommend you stop by your local Advance Auto Parts to have your alternator tested for free*. Or, at any point that you decide you don’t have the time, the tools, or the know-how to handle this at home, Advance Team Members are ready to help you. Find an Advance Auto Parts store close to you, or use our convenient mobile app to get the right parts.  

*Car battery testing and installation available on most automotive vehicles, at most locations, unless prohibited by law.

How To Test a Car Battery
Last updated August 17, 2022