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Bad Battery or Bad Alternator: How to Tell the Difference


You know the feeling when you put the keys in your ignition, turn them, and the car doesn't start. What about when you're driving on a busy road and your car stalls? Is it a bad battery? A bad alternator? How can you tell the difference?

This article highlights the differences between bad batteries and bad alternators, how to notice which is which and if you can drive with defective batteries or alternators. 


Functions of Batteries and Alternators

A car battery sits in the hood of a car near the engine and alternator. It sends a signal to the motor to start the engine and tells the ignition to combust fuel. 

The battery supplies energy when a car is off. A misconception is that car batteries power radio, lights, windows, and windshield wipers, but the alternator provides most of the energy when a car is on. 

The alternator helps charge the battery while the car runs. You can drive a car with a bad alternator, and a bad battery, but you won't get very far since they depend on one another. 


Bad Battery 

Batteries and alternators work together to operate your vehicle, so when you have an issue, it can be difficult to pinpoint whether the alternator or the battery is bad. 

Batteries last between three and five years and cars with bad batteries take a long time to start. The engine won't turn over if there isn't enough charge in the battery, or the car takes a long time to start.

Dim dash lights and headlights can indicate a bad battery. If they are dim or out when the car is off, you could have a bad battery


Bad Alternator Guide 

The main way to tell if your alternator needs attention is when the charge button lights up after you've started the car. The red charge icon shows a battery symbol with a plus and minus on either side. 

If your car stalls a lot, it might be a faulty alternator. 

Other things to look out for are dim headlights and dim dash lights. The alternator delivers a power source to the lights in the car when it is on. If the lights dim or flash, chances are the alternator isn't working.

Any electrical issue or strange noise can show a failing alternator. 


How to Test Which System is Faulty

Unsure if you have a bad battery or alternator? Try this test.

Turn the car off and grab some jumper cables to start the car. Two options can arise with this test.

  1. The car will start and then stall, showing an issue with the alternator.

  2. The car won't start at all, but other systems such as the lights or radio work. This means your car has a bad battery.


Need a New Battery or Alternator?

Finding out your car has a bad battery, or a bad alternator takes a lot out of you. Luckily, we at Prairie Battery can help you find one of the best replacements. We offer AGM and flooded types of batteries to customers. 

Next time your car stalls or the engine won't start, feel free to reach out to Prairie Battery.


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