What Does the Alternator Warning Light (Battery Warning Light) Mean?

How Conventional Vehicle Batteries Work

Batteries are used to store energy to keep the veh

Batteries are used to store energy to keep the vehicle and its power accessories working. Chemical energy stored in the battery is how the vehicle can be started initially and then as it runs, the battery is recharged. 

Recharging happens when the crankshaft pulley turns the alternator belt (also known as serpentine belt or accessory belt) which spins a rotor inside the alternator (which is sometimes referred to as a generator).

The alternator takes kinetic energy from the rotating pulley and converts some of this energy into AC power, which is then converted into DC current and stored in the battery. This energy is then used to power things such as headlights, power windows, heated seats, radio, air conditioner, DVD players, and cell phone chargers.

Note: Older vehicles may use a dynamo (also called a DC generator) instead of an alternator.

The voltage regulator maintains the desired voltage while charging the battery. It is often a component of the engine control unit (ECU).

The current (made of electrons) flows from one post of the battery, through the accessories, then into the other battery post. Various wires around the engine bay called ground straps connect parts of the wiring harness to the chassis, which help complete different circuits.

Battery Light FAQs

You have the questions, The Drive has the answers!

What Does It Mean When the Battery Light Comes On?

It means there’s an issue with the vehicle’s charging system, which includes the battery, the alternator, the wires, and the ECU.

Is It Safe to Drive My Car With the Battery Light On?

If something in the vehicle’s charge system isn’t functioning properly, there is risk of the car shutting off without warning. It’s also possible that if the vehicle dies, it might not be possible to start it back up. Because of this, we do not recommend or suggest driving with the battery light on to any place other than back to your house or a service center. If the light comes on before driving, we do not recommend driving.

What Do You Do When the Battery Light Comes On? 

Slowly drive your car home, to a service center, or to an auto parts store. Then, diagnose and fix.

How Can You Tell If It’s the Battery or the Alternator?

Use a multimeter to check the voltage on both the battery and alternator to verify they’re functioning at the correct levels.

Will a Car Start With a Bad Alternator? 

It is possible for a car to start with a bad alternator, but it will likely immediately die.


3 FAQs About Battery Light Activation

Here are answers to the three most commonly asked questions related to car battery light activation:

1. How Does A Vehicle Battery Work?

A vehicle battery stores and converts chemical energy into electrical energy (electricity).

Usually, your car battery would contain a set of six electrochemical cells that generate a total of 12 Volts.

The vehicle’s battery powers the ignition system, air conditioner, interior lights, power windows, and more. Essentially, the battery brings to life the different electrical components in your vehicle!

But won’t the battery run out of juice from powering so many things?

Typically, it wouldn’t. 

And it has to do with how your vehicle’s battery system works:

  • Once the battery starts your engine, a component known as the crank pulley uses the power generated by your engine to turn the alternator belt or serpentine belt
  • This alternator belt then spins your alternator, power steering pump, and more to generate kinetic energy
  • The alternator then converts this kinetic energy into electrical energy
  • And the electrical energy is used to charge your vehicle’s battery, power your interior lights, and do so much more

In short, once the engine is fired up, the vehicle’s battery usually has the means to charge itself.

2. What Does The Battery Light Do?

Every time you start your car, the dashboard lights come on. This includes the check engine light, brake light, coolant warning light, power steering light, the battery dashboard warning light, etc.

And, in a few seconds, these lights would go off. 

However, if the car battery light (aka charging system light or battery indicator light) doesn’t turn off for some reason and stays on while you’re driving, you might have a problem on your hands. 

The battery light staying on is your vehicle’s way of indicating that there are issues with the:

  • Battery voltage or battery power that’s generated
  • Battery charging system
  • Electrical system or electrical components, etc.

3. Is It Safe To Drive With My Battery Light On?

While it could be possible to drive your car with the battery light on, we advise against it.


Chances are that your vehicle’s battery is running on whatever juice was left from the last battery recharge cycle. But there’s a high chance that the battery power will get drained entirely, and your engine may stop running.

Essentially, you might not be able to drive for very long with the battery indicator light on.

Moreover, if you turn off your engine, you may be unable to restart the ignition system without:

  • Jump starting your battery with jumper cables
  • Fixing the underlying issue causing the car battery light to come on
  • Or getting a new battery for your vehicle

What Is a Car’s Charging System?

A modern vehicle’s charging system, which functions to keep the battery charged, includes a battery, wiring, an alternator, and the electronic control unit (ECU). Older vehicles also had a voltage regulator.

Alternator: The alternator accepts mechanical energy from the engine and turns it into electrical energy to power accessories and charge the battery.

Battery: The battery provides energy to start the vehicle and to power its electronics.

ECU: The electronic control unit, not to be confused with the engine control unit, is a device that manages the linked electronic system. It regulates where, when, and how power is held or flowing.

Three types of electrical testers., DepositPhotos

Is it safe to drive with the alternator warning light on?

When this light is illuminated, your car is still somewhat safe to drive as you will have enough battery power to run the engine. However, it is still dangerous to continue driving for long distances or at high speeds as the battery will run out of juice and the car will be harder to stop without the assistance of the engine. If you are on the freeway and this light comes on, you should pull off the freeway and move to lower speed areas as soon as possible.

As always, our certified technicians are available to come to you to help you diagnose any issues with your car’s battery.

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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