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How To Know If The Alternator Or Battery Is Bad? A Comprehensive Guide

How To Know If The Alternator Or Battery Is Bad

If you're wondering “how to know if the alternator or battery is bad,” if your engine starts and dies immediately, it might indicate the alternator is not charging the battery properly.

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The vehicle's battery and alternator play a significant role in charging the electrical systems and getting your vehicle started. When any of those go bad, they might impact how you start your car and lead to difficulty starting.

Understanding which one of those components is the root culprit helps you undefine the expected repair costs and options. Therefore, it is critical for you as a driver to understand the main differences between the two components and how to identify which one of them is causing the issue.

This article is a comprehensive guide to help you differentiate between what problems expect from a bad battery and an alternator. This way, you'll get a general idea about when to replace the battery and when to replace the alternator.

What's the difference between the alternator and the battery jobs?

Before we dive into the details about which one is faulty in your car, whether the battery or the alternator, it's important for you as a car owner to understand the difference between each one of those components jobs. By understanding their job, you'll immediately expect what could go wrong when they go bad.

There is a common misconception that the battery is responsible for charging the electrical components in your car; if they're not working, you have to replace the battery. However, the battery is only used to start your vehicle and provide this initial charge to get the engine cranking.

After the engine is running, it's the alternator's job to start charging the electrical components, including recharging the battery. Hence, it's ready to start your car the next time you want to.

As you might notice, both the battery and alternators can have an impact on the optical components, but one of them is used when the engine is running and one when the engine is not.

How do we know if the alternator or battery is bad?

Now you have a general idea about the role of both the battery and alternator in your car, the next step is to understand what could go wrong when each one of those goes bad and how exactly to differentiate between a bad alternator and a bad battery because it can cause a lot of confusion.

1-   Signs of a bad battery

When your car battery goes bad, it will result in several symptoms that could help you take a look at the battery and identify whether it's going bad or not:

Slow cranking

The first and most critical thing to happen when the battery is about to go bad is the slow cranking. You'll eventually get a final cranking, but it will be much slower when the battery weakens. However, if the battery is completely damaged, you won't have any cracking.

Dimming lights

Another thing you'll notice is that your headlights and doom lights are very dim. Remember that this happens only when the engine is turned off. In other words, if the engine is turned on and you have dimming headlights, that might not be related to the battery.

Clicking sounds

If you tried turning the key in the ignition and realize there are only clicking noises, it's mostly related to a bad starter motor. Still, it could also be that the battery is not providing enough charge to get the vehicle cranking.

Electrical components malfunction

In some instances, a bed rattery might result in some issues in the electrical system components. Therefore, if you have any minor damages, you might want to check on the better and confirm that it's providing them with what's needed from the electrical supply.

how to know if car battery needs to be replaced

2-   Signs of a bad alternator

Similar to the batter, if the radiator is going bad, comment all also provide you some symptoms indicating that you have to replace it as soon as possible:

Warning lights

In general, a bad alternator typically results in some warning lights on the dashboards. These warning lines might be specifically related to the alternator depending on which vehicle you drive, but in general, it can be just a check engine light illuminating.

Regardless of the reason for check engine light elimination, you should not ignore the problem because it could be linked to a major internal issue. Therefore, you must scan your vehicle's internal computer and determine why the engine light is illuminating.

Suppose you confirm it's a bad alternator. In that case, you have to replace the alternator immediately because you'll suffer from many problems, especially those related to the starting issue when the alternator cannot charge the battery.

Dimming headlights

Although he indicated that the dimming headlights are typically related to a bad battery, that is true when the vehicle is turned off. In other words, if the battery is not used when the engine is running, you'll have to check on the alternator.

Strange noises

Another problem you might experience when the alternator is bad is some weird noises. Typically, these noises are going to come from the location of where the alternator is located. They will be more like grinding and squealing and getting that the alternator is about to fail.

Electrical system failures

Finally, since the alternator is responsible for charging all the electrical components, it's not surprising to deal with major electrical system damage socially if you're driving a vehicle with sensitive electrical components.

When To Replace Your Car Battery

How to test the battery And the alternator?

If you suspect that the battery or the alternator is going bad, you can perform more detailed inspections that could help narrow down and pinpoint the true culprit.

If you're looking to test any of those, you might want to consider the following general tests:

How do you test a bad battery?

Most mechanics perform two common tests to determine whether the battery is in good shape. The first is called a voltage test, where you connect a multimeter and look into the battery's current voltage. Typically, the voltage should be around 12.6 volts, but if that's not the case, then the battery is bad.

Another thing you could test is what's known as the load test, which is where you can inspect the ability of the battery to perform and provide the required charge when it's under load. This is a more complicated test that requires some help from a professional.

How do you test a bad alternator?

Like the battery, you can also perform tests or inspect the current alternator performance. One of the most common ones is what's known as the voltage test, where you can use a multimeter to see if the alternator has the right voltage or not. Typically, the alternator should produce between 13.8 and 14.2 volts; if that's not the case, you need to replace the alternator.

Your mechanics might even perform more thorough inspections using the amperage test. This allows them to check on the alternative capacity of producing the required charge and confirm that it's working as it should.

When Do I Need to Replace My Battery

Once you perform these tests, you can identify the faulty components. If you can identify them, you should replace them immediately. The more you wait on those problems, the harder it gets for you to fix the issue without needing to replace major components.

For example, your mechanic might identify that the battery has a lot of rust, and by cleaning it, it will work again. Therefore, you don't have to worry about replacing a full battery. On the other hand, if you decide to leave the problem for a long time, things can get more complicated, requiring installing a brand-new battery.

Reset Car Computer After Replacing Battery

How do we know if the alternator or battery is bad? Final Thoughts

There's a common misconception between a bad battery and a bad alternator when your vehicle shows the same symptoms. Therefore, it's important for you as a car owner to understand when it's the alternator versus the battery.

As we had discussed in this article when the alternator is bad, it'll impact the electrical components when the engine is running; still, if you can't start your car or if the vehicle starts slowly, it could mostly be the battery, but also it could be linked to a bad alternator that could not charge the battery.

Regardless of where the problem is coming from, your mechanic needs to identify the faulty component and replace it immediately before things get out of hand and further damage sensitive electrical components.

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