why does car voltage fluctuate when driving?

Why Battery Gauge Drops While Driving and What to Do

06/19/2021 by Aaron Johnson

The battery gauge drops while driving is not that complicated issue in your car. By testing some of your car’s components, you can find out why your car battery gauge fluctuates.

In this post, I will tell you why your car battery gauge goes up and down and how you can fix the battery gauge.

So, let’s break down why this is happening:

Why Battery Gauge Drops While Driving

battery gauge drops while driving
Why battery gauge drops while driving

First of all, you need to know what the battery gauge actually is. I know many of you already know what a battery gauge is. A battery gauge or battery indication is a device that gives you information about your car battery. In your car, you have lots of gauges on the dashboard. One of them is the battery gauge.

The battery gauge always tells you the current state of your car battery. If anything happens to your car battery, that you can see on your car battery gauge. That’s why reading and understanding the battery gauge in your car is important.

A bad alternator, battery’s health, and corrosion around the battery are the main reasons why your car battery voltage drops while driving. To know the main reasons, you have to check all of these components in your car.

A Bad Alternator

The vehicle alternator is an electric generator. A car alternator’s job is to charge the car battery and provide power to the electronic system in your car.

If you have a bad alternator or a overcharge alternator in your car, many issues you might face. For car battery voltage fluctuating, your car battery’s shape is not only a culprit. An alternator can be the main reason why your car battery gauge fluctuates while driving.

bad alternator
Bad Alternator

As you know, through an alternator car battery gets charged. Vehicle alternators take the mechanical power from the engine and turn it into electrical energy to recharge the battery.

Bad alternators can’t properly distribute the electrical energy in your car’s electronic system and into your battery. So, if the alternator can’t provide enough power or charge, and that’s why the battery gauge goes up and down.

1st: Check the Alternator Properly

When your car alternator charges the battery, by spinning the alternator, it charges the battery. To spin, the alternator needs a belt (also called a serpentine belt). When you check the alternator in your car, the first thing you need to check is the alternator belt (Serpentine belt).

An alternator belt should be in the proper place and also work efficiently. That’s why you should check the alternator belt first. Another thing you need to do is check the tightness of the alternator belt.

The alternator belt needs to be tight enough to transfer the power from the engine to the alternator. The alternator belt issue is not rare; this can happen in any vehicle. Too loose belt slip when alternator tries to spin. That’s why alternators can’t work properly.

If you see your car’s alternator belt looks too old, with any visible damage, and too loose to spin, then you need to charge the alternator belt. An alternator belt will cost you around $30 to $60, and labor costs depend on how long it takes to change the belt. The total replacement cost of an alternator belt is typically between $120 to $180. To replace the alternator belt, I highly recommend you go to an auto service point.

Make sure the alternator belt is tight. Too loose a belt prevents the alternator from spinning, and eventually, the alternator won’t work properly. But you also make sure the alternator belt is not too tight. Too tight alternator belt can break out so quickly.

2nd: Test the Alternator

After you check the alternator’s belt and measure the belt tightness and belt condition, even though your car battery gauge moves back and forth, then you need to test the alternator.

Testing the alternator is quite simple, and anyone can do it. The easiest way to test an alternator is using a voltmeter. Let’s see how you can test your car alternator:

How to Test an Alternator

Below you will see how to test an alternator properly by using a voltmeter. You need to follow the instructions below step by step:

  1. To test an alternator, first, you need a voltmeter.
  2. Check the car battery voltage with the engine off. The battery voltage should be between 12.5 to 12.8 volts. If battery voltage shows less than 12.4 volts, this means your car battery needs a charge. Charge the battery if the voltage is low before conducting the alternator test in your car.
  3. Start the engine and recheck the voltmeter. If you see that the voltmeter shows between 13.8 to the 15.3-volt range, this means your car alternator is in good shape.

This is how you can test the car alternator. After you check the alternator and test the alternator but couldn’t get the issues, that means your car battery gauge is jumping for another reason.

The battery is Not in Good Shape

The battery gauge reading on the dashboard is all about the battery. If the battery is not in good shape, the battery gauge will show car battery voltage fluctuation. Checking the car battery can be another solution for battery gauge reading.

After a long time, the car battery is getting out of order; for any battery, age is matters. A better-quality automobile car battery can provide power and work effectively for around 4 to 6 years. That’s why whenever you buy a car battery, you should buy a car battery from the best places.

Car batteries can get damaged for other reasons. Always avoid any damage to your battery. Regular maintenance of your car battery can avoid any damage.

Check your car battery properly. The battery should not be too old and not get that hard damaged.

Batteries Corrosion

We are familiar with corrosion, especially when it’s about batteries. Corrosion damages the battery and prevents the battery from producing the maximum amount of power to the car.

Open the car battery hood and observe the condition around the battery. An alternator and a battery connected by wire; that’s why you need to check those wires for corrosion.

Another thing you also make sure the connection between an alternator and battery is alright. A loose wire connection is not applicable to your car battery.

Keeping the battery clean is simple. A bad connection between the alternator and battery and corrosions around the battery can cause battery gauge drops while driving.

Why Battery Gauge Drops When AC is On

The battery gauge drops when AC is on because of the alternator in your car, especially if your car has a one-wire alternator. When you run the car air conditioner, it draws 70+ amps, and one wire alternator does not sense that high draw.

For those who don’t know what a one wire alternator is. One wire alternator means a single wire used to connect the alternator to the battery. There are no other wires that need to be connected to the electronic system in your car.

An alternator needs 14 to 15 volts to compensate for the extreme voltage that you are experiencing in your car. When you turn on your car AC, it consumes high voltage for the battery, and the alternator job compensates for that voltage in the battery. That’s why a one wire alternator is not that powerful to pay for this amount of voltage.

Most of the time, alternator performance causes the battery gauge to go up and down. Bad alternator performance and loose connection between battery and alternator cause for battery gauge drop when ac is on.

Why Battery Voltage Drops When Accelerating

If your car battery voltage drops when accelerating, this means something is drawing more current during acceleration. You need to detect which component of your car draws the current most when you are accelerating.

What to do if battery voltage drops when accelerating:

  • Battery Voltage Measurement:
    Fully charged car battery voltage should be around 12.6 to 12.8 volts. That’s why if your car battery voltage is less than 12.5 volts, this low voltage can cause battery voltage drops when accelerating. You need to make sure the battery voltage goes up to around 13 V.
  • Turn Off All the Components While Accelerating:
    When you turn on the car air conditioner in your car, the AC in your car consumes voltage from your car battery. Car air conditioners and all of the electrical components you turn on in your car take voltage from the battery. That’s why when you accelerate the car, try to turn off all the components that consume the voltage.
  • Check The Alternator:
    Whether your battery voltage drops while driving or the battery gauge fluctuates at idle, you need to check the alternator in your car. When it comes to battery voltage issues in vehicles, an alternator can play a prominent role. That’s why if the battery gauge goes down when accelerating, you need to check the alternator properly.

Frequently Asked Questions (FAQ)

Q: What should battery voltage be while driving?

Ans: A fully charged car battery voltage should be 12.6 volts or above. But while you are driving your car, the battery voltage should be higher than that. When you drive your car, the battery voltage should be between 13.7 to 14.7 volts. If the car battery voltage shows a lot less than 13.7 volts while driving, you should check your car alternator.

Q: How many volts should a car battery lose overnight?

Ans: Losing battery voltage overnight depends on the battery’s health and storage ability. When the car engine is running, battery voltage should be above 13.6 V, and 12.6 V should be when the car engine is off. Battery voltage can be 12.1 V in the morning; the rest of the voltage can be lost overnight.

Q: Is it normal for battery voltage to fluctuate?

Ans: The battery voltage fluctuation is totally normal. Battery voltage fluctuates because of using different types of accessories. But battery voltage going too low or too high is not normal at all. To avoid any issue with your battery, you have to check the battery voltage regularly.

Final Word

Now you know what caused the battery gauge drops while driving. The battery gauge fluctuation happens not only for car batteries, and there can be other reasons.

An automobile battery is the fundamental part of a vehicle. Your whole car’s electrical system is connected to the battery. That’s why there is no chance to avoid any battery issues in your vehicle.

Whenever your car battery gauge goes up and down, and you notice too high and low fluctuation, you have to check the car alternator first. If you find any issue with your car alternator, you have to fix that issue right away.

Every time an alternator is not the culprit. Battery wire connections, corrosion, and your battery’s state can be the main culprit; that’s why check all of the components connected to the battery.

I hope now you know why your car battery gauge drops while you are driving. If you have any future questions about the battery gauge (battery indicator), let us know in the comment below. Thank you for visiting my blog. Have a good day.

Source: https://caralso.com/battery-gauge-drops-while-driving/

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