The Difference Between a Dead Battery and Bad Alternator

Last Updated on June 24, 2019 by themechanic

When you start having electrical problems with your vehicle, you will notice them rather quickly. You could be driving along on the road and then suddenly see the lights on your dashboard flicker or shut off completely. Soon after, your entire vehicle may stall which forces you to pull over to the side of the road so that you don’t get stuck in traffic. This is certainly an inconvenient situation that every driver wants to avoid.

There are two likely reasons as to why you would have these electrical issues. You would either have a dead battery or a bad alternator. It may not always be easy to tell which one you’re faced with because the symptoms tend to be similar. After all, the battery and alternator are both responsible for producing electricity. They just produce different amounts of electricity and provide power in different ways.

Contrary to popular belief, the car battery does not supply power to all the electrical components of the vehicle. That is the job of the alternator. However, the alternator cannot start the vehicle because the mechanical energy of the engine is what keeps the alternator running. Therefore, the car battery and starter motor are needed to get the engine running which, in turn, allows the alternator to run.

When you put your car key in the ignition keyhole and turn it, the car battery sends an electrical current to the starter motor. If the current is as strong as it’s supposed to be, the engine will turn on and its components will start moving. This activates the alternator which generates electrical power for all the other electrical components of the vehicle, such as the air conditioner, radio, GPS, etc.

The battery does serve as a power reserve for these components in case the alternator is failing. But if the alternator dies completely, the battery will die soon afterward because it is not powerful enough to supply electricity to all these components on its own. Even a new car battery would die within minutes if it was the only source of power for them.

Dead Battery or Alternator?

Okay, so how do you know for sure if the alternator died first or if the battery died? Well, if your vehicle dies, the first thing you should do is jump start the battery. If the vehicle starts up and you’re able to drive it to a mechanic or auto store, then your battery is bad and must be replaced.

If the jump start doesn’t work and your electrical components still fail, then you have a bad alternator. Sometimes the jump start may work but then your vehicle will stall after a couple of minutes. This also means your alternator is at fault. A jump start provides the electric current needed for the starter motor to get the engine running. After that, you should have plenty of time to drive to a mechanic if the alternator is functional.

Don’t forget that a dead alternator will soon cause a dead battery too. This is where people tend to get confused because they’ll drain their battery of its power after their alternator dies without even realizing it. Then, they go to test the battery with a battery tester device and see the battery is dead. So naturally, they think the battery is why the vehicle failed. But what this doesn’t tell them is that the dead alternator may have been the reason for it.

Read also:

If you perform the jump start test, that is the best way you can know which component is truly dead. There are jump-start devices you can purchase to do the jump-start independently or you can do it the old-fashioned way and have somebody give you a jump start through their car battery. Either way is fine.

Leave a Reply