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Car Battery Lights 101: Underlying Causes & and Easy Fixes

What To Do When The Battery Light Comes On
Last Updated on Aug 16, 2023 By Lillian Kazmierczak

Nothing is worse than a warning light coming on while you are driving. But when the battery light comes on, it is worse. Understanding why the light comes on and what to do will help ease that anxiety. Here we look at why the battery light comes on, what to do, what causes the light to come on, and how to fix the problems that cause the battery light to come on

What Is Happening the Battery Light Is On?

Think of the battery as the vehicle’s storage for energy. It then converts this energy by the continuous rotation of the alternator/serpentine belt. At the same time, it powers your air conditioner’s compressor, power steering pump, alternator, and possibly the water pump with electricity that your vehicle uses to recharge itself.

When the light comes on, one of three things is not working correctly. There is an issue with the electrical components or the electrical system. The system charging the battery isn’t working, or there is an issue with the battery power or voltage.

What should I do now?

1. Eliminate any unnecessary use of the battery

You need all the battery power you still have. Unplug your phone, turn off the air conditioning/heat, and leave your power windows as they are. Only use what is needed, like the windshield wipers or headlights. You still want to be as safe as possible.

2. If you are close to home or a mechanic, drive there

When the light comes on, you only have 5 to 30 minutes of battery power. That is a significant difference in time. Getting to safety is essential, so keep driving if you are close to a mechanic or your house.

3. If you still have a long way to travel

Pull over in a safe area if you’re not close to where you’re going. You don’t want the car to die in the middle of the freeway or at a 4-way stop. Then turn the car off. It probably won’t restart, so you will be there for a while.

4. Call for assistance

If you are not mechanically inclined and have a toolbox in the car, you will need help. Call for a tow truck or someone that can help you in this situation.

Causes of the Battery Light Coming On

Causes of the Battery Light Coming On

Blown fuse

A blown fuse is the easiest problem to fix and the least expensive. You can replace a fuse in minutes. Check the manual for the fuses that affect the battery. This will make your search much easier.


  • Package of new fuses

Step 1: Locate the fuse box, usually found on the driver’s side below the dashboard. To locate the fuse box and what the fuses are for, check the owner’s manual

Step 2: Pull each fuse out to see if the fuse is broken or burnt. A good fuse is shining silver.

Step 3: Replace the blown fuse with a new one. Fuses are color-coded by amperage, so if you blow a green fuse, you replace it with a green fuse. Some cars have a few spare fuses in the box. If not, you can purchase them online or in a store.

Once the fuse is changed, it should last for years. If it blows again, there may be an issue with the system that is blowing a fuse. Have a mechanic look at it.

Battery terminal corrosion

Corroded battery terminals affect the conduction of electrical current. Poor conduction results in a poorly charged battery. This is another quick, easy fix that is inexpensive.


  • Wrench
  • Baking soda
  • Water
  • Brush or stiff toothbrush
  • Dry cloth or rags

Step 1: Remove the battery cables from the terminal to avoid getting shocked by loosening the bolt on the negative (-) terminal first. Loosen the bolt and pull the cable off the terminal. Then remove the positive (+) cable. While looking at the battery, check it for damage and leaking.

Step 2: Take an old toothbrush or stiff brush and brush around the terminals removing the corrosion and debris. If stubborn corrosion occurs, sprinkle baking soda on the terminals and wet the brush to remove the remaining corrosion. Once clean, take a damp cloth and remove any baking soda. Then dry the terminals with a clean cloth.

Do not get the baking soda/water on the rest of the engine.

Step 3: After the terminals are dry, apply a generous amount of Vaseline to the terminals and reattach the battery cables to the battery, starting with the positive cable. Once they are reattached and tightened, start the car to ensure the battery terminals were the problem.

Faulty Battery

Batteries wear out with time, most last for 3 to 5 years, but cold weather and other things can affect the battery’s life. A faulty battery no longer stores energy or powers the vehicle. Checking the battery is quickly done with a multimeter.


  • Multimeter

Step 1: With the hood up, locate the two wires coming from the battery.

Step 2: Place the multimeter’s black probe on the black negative battery terminal and the red multimeter probe on the red positive terminal. In case the battery is good, the multimeter reading should be 12.6 volts. A reading of lower than 12.6 tells you something is wrong with the battery or the alternator is not charging. Below we will test the alternator.

If the battery needs replacing, one can be purchased and replaced by removing the cables from the terminal after loosening the cables with a wrench. Pull out the battery and put in the new battery, then place the wires on the terminals and tighten them.

The alternator is faulty if the car doesn’t start after replacing the battery.

A faulty alternator

The alternator charges the battery, so if it is faulty, it will not charge the battery. 13.6 to

14.6 is the needed voltage to charge the battery. Using the multimeter, you can check the alternator’s voltage.


  • Multimeter

Step 1: Start the vehicle and let it run for 10 minutes. If the battery is dead, the car won’t start. You can jump the car to get it started and let it run the 10 mins. If you can’t get the car started, it must go to an auto shop.

Step 2: After the car has idled the 10 mins, place the multimeter probes on the battery terminals- black to black, red to red. If your reading is higher than the last battery reading, the alternator is working fine, and the battery is your problem. If there is no reading increase, the alternator isn’t charging your battery and needs replacing.

Replacing the alternator is time-consuming, and you should know what you are doing if you are going to change it. Sometimes it is wiser to let a professional do the job.

Faulty alternator/serpentine belt

Alternator/serpentine belts eventually crack and break. Once this happens, the battery cannot recharge because the alternator won’t rotate. You will not have vehicle accessories that require battery power, including power steering and air conditioning. If the belt brakes while driving, the car will stop immediately. Serpentine belt replacement isn’t hard, but if you haven’t done it and don’t have the tools, let a professional do it.


  • New alternator/serpentine belt
  • Ratchet and sockets
  • Belt placement tool

Step 1: Disconnect the battery. Remove the engine cover by releasing the clips if needed. Look at the belt placement before you start. Taking a picture will ensure you properly place the belt as it snakes around several pulleys.

Step 2: Use a ratchet and socket on the pulley bolt. Then rotate the tensioner arm as far as possible to release the tension on the alternator/serpentine belt. Remove the belt and release the tensioner.

Step 3: Faulty tensioner and idler pulleys won’t hold the belt in place. Examine to ensure they are in proper alignment. Then spin them to ensure they are not squeaking and move freely. You can brush around the pulleys to remove any debris that will cause issues later.

Step 4: Use the belt replacement tool to weave the new belt through the pulleys.

Step 5: Loosen the tensioner pulley using the wrench. Then pull the belt over the tensioner. You may need help to get the belt on the tensioner. Now readjust the pressure on the tensioner to keep the belt in place.

Step 6: Once the belt is in place, replace the engine cover. Reattach the battery cables to the terminals and start the car to ensure the belt is working correctly.

Bad battery cables

Faulty battery cables won’t transfer the battery power to the car/truck. Cables that are too loose, broken, or cracked interfere with the flow of electricity. If the battery cables need replacing, follow the steps below.


  • New battery cables
  • Wrench

Step 1: Look at the current battery cables and follow them with your hand to see where they connect. Compare the new ones to the old ones to ensure they are the correct cable and the right length.

Step 2: Remove the battery cables starting with the negative cable, then remove the positive cable. Once the cables are removed, pull the battery out of the vehicle.

Step 3: Remove the negative battery cable from the engine using the wrench once the battery is removed. Then remove the positive cable from the fuse box or starter. Again compare the old cables to the new cables ensuring they are the same.

Step 4: Bolt the new cables in place, the negative to the engine and the positive to the fuse box or starter. Ensure the bolts are tight for the best electricity flow.

Step 5: Place the battery back into the car. Connect the new cables to the battery terminals starting with the positive (red) terminal, and tighten them. Before attaching the cables, ensure the terminals are clean and debris-free.

Step 6: Once the cables are tight, start the car to ensure the battery is working.

Wiring issues

There are multiple wires involved in the electrical system of your vehicle. Broken and cracked wires can result in a short or complete loss of power. Unless you are a mechanic, this is an area that should be taken care of by a mechanic. Working with the electrical system can lead to burns and being shocked. Leave this to a professional!

Too many accessories

All accessories pull their power from your alternator. Too many accessories in use will draw the energy from the alternator and slow the charging of the battery. The battery light will then come on.

Be selective in your accessories, especially on hot summer days when the air conditioning is running.

About the author

Lillian Kazmierczak

As far as I can remember, I would say I have been a car nut for my whole life. My father was a car dealer who used to change and repair his cars himself. This gave me the opportunity to get around all sorts of cars and get my hands dirty repairing vehicles from an early age.

A great fan of Japanese quality and German preciosity, my deep passion lies in older models that I believe have a flair that takes me back to my childhood! I also love their extraordinary durability and reliability when compared to today’s modern models.

When not out taking a ride, I enjoy socializing with fellow motorheads online and consuming any car facts and figures I can get my mind on!

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