How to Test an Alternator by Disconnecting the Battery?

A very important part of a car is its alternator. It converts the chemical energy of the car into electrical energy. It uses the engine power to run the car as well as charges the battery for later use. 

If your car’s alternator breaks down in the middle of the road, you may get in trouble. Of course, a faulty alternator cripples the car. This is why many people search the internet to find out how to check an alternator. 

There are several ways to test if your car’s alternator is working properly. One of those is testing by isolating the battery. This is a very fast method. So in this article, we will discuss how to examine an alternator by detaching the battery. 

Symptoms of a Faulty Alternator

An important point before starting the test – you have to look for different types of confirmation indicators because this problem is always predictable in different places.

However, how do you know if the problem is related to your car’s alternator? Of course, there are some symptoms, the most common of which are:

Engine Shutdown

You are driving your car and passing quality time. Suddenly the engine stopped. Yes, this can happen if there is not enough energy for fuel injection.

Service Engine Light Lits

This signal can be seen when looking at the car’s dashboard. Although it is different according to the car model. However, when you release the alternator, the check engine light is illuminated.

Dim Light

One of the most common symptoms of a poor alternator is dim light. You can see this clearly, especially at night. This feature can be noticed in headlights as well as center lights and dash lights. Whenever the RPM of the car increases, the lights are also illuminated periodically.

Weirdest Noise Is Made

The car alternator has a serpentine belt. It extends over time, causing the alternator crane not to rotate properly. It reduces the load on the engine. And when the load is low, squealing sounds occur and alternator bearings become worn and also make strange noises.

Battery Dies

When a car’s alternator is turned off or faulty, the battery’s performance quickly deteriorates and it dies. So batteries must be checked regularly. Otherwise, the cars will be damaged.

Electrical Problems

Different electrical parts of the car can cause problems such as slow working. Due to lack of power, the equipment will not turn on at all or may suddenly turn off while running such as radio.

Cost to Fix an Alternator

How much it costs to fix or buy an alternator varies depending on the vehicle. If you want to buy a small alternator, it will cost around $100. This cost will increase many times over in the case of a large and powerful alternator.

How to Test an Alternator by Disconnecting the Battery?

So here we are about to learn how to test your car alternator easily and quickly by disconnecting the battery. Pay attention and follow the steps.


The first step is to park your car in a safe and open place, such as a driveway.


Lift the hood of the car. Make sure the car is in stable condition.


Go to the driving seat of the car.


Turn on the engine. Defective alternators can cause some problems when starting the car.


When the car starts, get up from the driving seat and go back to the car battery.


Notice if there is any dirt or corrosion around the battery. If so, clean it up.


Disconnect the positive connection of the battery while the vehicle is on.


Now notice if the engine of the car is running as before.

Okay, the handiwork is almost over. Now you just have to observe. There is nothing to worry about if the car continues to run even if you disconnect the positive connection of the battery at the time the car is switched on. The alternator is OK. In this case, the problem is probably in another part. 

On the other hand, if the car shuts down after disconnecting the positive connection of the battery when the car is on, then it must be understood that there is a fault in the alternator. This is because the alternator that has any problem is unable to supply power to the engine.

Is This Method Safe to Test an Alternator?

It is easy and quick to test the alternator by disconnecting the battery in all of the methods. But there are some problems. Our researchers have expressed doubts about the effectiveness of this method. 

The method of testing by disconnecting the battery is suitable for a generator. From this point of view, an alternator is not a generator. This is because when you disconnect the battery and test your car’s alternator, the regulator is more likely to malfunction. This is the significant risk of this method.

Any Alternative Methods That Are Comparatively Safe?

Of course, there is. You can test your car alternator more securely without disconnecting the battery cable. In this case, you need to utilize a voltmeter. This is a relatively reliable and innovative method. Follow the steps below to make it effective.

Step 1

Switch on the engine and turn off all other electrical components.

Step 2

Take a voltmeter. Go to the car battery and take readings between the terminals.

Step 3

Now turn on the electrical equipment and take the reading again.

Just 3 easy steps, right? Now, look at the result. If the reading is 14V when the electrical components are off, then your car’s alternator is OK. 

Understand that there is no problem with the alternator even if the reading shows 13V later i.e. after turning on the electrical components. 

But if there is anything different from all these reading results, then it is a matter of concern. However, be careful throughout the test and keep the car in a safe place.

How to Maintain an Alternator From Going Bad?

You know the importance of an alternator for a car very well. So it is your responsibility to take proper care of this part. The question here is how you can take care of the alternator. No worries, they are given below.

Check the Electrical Connection

Sometimes all the devices are fine but the connections get loose causing various problems. So you should check all the connections associated with the alternator. If there is a connection that is loose or missed, fix it.

Check for Any Damage

If there is a fault in the alternator, it will not be able to charge the car battery. So check if there is any such problem with the alternator. See if the connections are tight enough. If the problem is serious, replace it as soon as possible.

Clean the Outside of the Alternator

Over time, lots of dust accumulates in the alternator. Excess dirt makes it overheat. To do this, wash the outside of the alternator with water and dry it well.


Now consider what you have learned from this article. You just learned how to test a car’s alternator by detaching the battery. With this article, you know what the symptoms of a faulty alternator can be. 

You learned how reliable this method is and whether there are any exceptions. However, there is only one goal in adding so much information to this article so that you can accomplish this task properly. 

After reading the article, you should not have any hesitation about it. However, before you resort to any method related to automotive, be sure to ensure safety and do not delay. 

In the case of an alternator, any delay will not be acceptable. If you get stuck somewhere, our advice is to take the advice of a pro. Hope you got all that you need to know. 

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