Should Battery Voltage Decrease While Driving?

If you notice that the battery voltage in your car is decreasing while you’re driving, then you may be wondering what the issues causing it are! In this article, not only will you find out what all the different issues are, but you’ll also learn how to treat them as well as other frequently asked questions!

So keep reading to find out everything you need to know!

Should Battery Voltage Decrease While Driving?

No, battery voltage should not decrease while driving. When your engine is running, the alternator in your vehicle recharges your battery as it runs. As long as the alternator is working properly and there are no other issues with the electrical system, the battery voltage should remain constant or gradually increase while you’re driving.

What Should Your Car Batteries Voltage Be While Driving?

The normal range for a car battery voltage is between 13.5 and 14.5 volts, then it’s a sign that your alternator is either overcharging or undercharging.

When the voltage is lower or higher, then it means that there is probably something wrong with the alternator

Why Does Your Battery Voltage Drop While Driving?

A Faulty Alternator

The most common cause of your battery voltage dropping while driving is a faulty alternator. When the alternator isn’t working properly, then it won’t be able to recharge your battery as you drive and the battery will gradually discharge over time.

How To Fix A Faulty Alternator

If you think that you have a faulty alternator, then you’ll either need to consult a mechanic or try to test the alternator yourself.

To test the alternator, you should do the following:

  1. Attach a multimeter to your car’s alternator. Put the red cable on the positive terminal and the black cable to the negative terminal.
  2. Once you’ve done that check the multimeter voltage. It should be 12.6 volts.
  3. If you notice that the voltage is below 12.4 volts, then it means that your battery needs charging.
  4. Now start the car up and check the reading again. If you notice that the reading is between 13.7 and 14.7 volts it means that the alternator is working correctly.
  5. If it’s over 14.7 it means that the car is being overcharged, and if it’s under 13.7 then it means it’s being undercharged.

Once you’ve identified whether there’s a problem or not, you can then decide how to fix the issue yourself, or go to a mechanic.

A Faulty Voltage Regulator

Another common cause of a battery voltage dropping while driving is a faulty voltage regulator. This part regulates the amount of current flowing from the alternator to the battery, and if it’s not working properly then it won’t be able to charge your battery correctly.

How To Fix A Faulty Voltage Regulator

If you think you have an issue with your voltage regulator, then you should take it to a mechanic. They will be able to identify the problem and help you fix it.

An Old Battery

If you notice that the battery voltage is dropping while driving it may be due to an old or worn-out car battery. If you’ve had your battery for 3-5 years, then the chances are that it may need to be replaced.

How To Fix An Old Battery

When your battery is old and worn out, the only thing you can do is replace it. Fortunately, this is incredibly easy to do, so you can either get a mechanic to do it for you or try doing it yourself.

The Car Has Been Left For Too Long

On top of an old car, it could be that you’ve left your car parked for too long and now the battery has lost some charge. Then this could be why the battery voltage isn’t as high as it should be.

How To Fix A Battery That Has Been Left Too Long

When your battery has been left for too long, the easiest thing you can do is use a trickle charger to charge it back up. If you don’t

A Faulty Battery

Just like a battery that has been left too long, another reason that your battery voltage may begin to drop when you’re driving is because the battery is simply faulty.

Unfortunately, when this is the case, then there isn’t really a fix. The only thing you can do is get a replacement battery.

An Old Serpentine Belt

The serpentine belt should be replaced every 50,000 – 100,000 years, depending on the usage and care. If you notice that the replacement for your serpentine belt is creeping up, then it may be time to consider a change!

What To Do About An Old Serpentine Belt

If you’re dealing with an old serpentine belt, then the best thing you can do is go to a mechanic to get the issue fixed.

Corroded Or Loose Terminals

If you have corroded or loose terminals, then this could also cause your battery voltage to decrease while driving. You should inspect the terminals and make sure that they’re securely fastened and not corroded.

How To Fix Corroded Or Loose Terminals

Fortunately, if your battery terminals are corroded or loose, then the fix is incredibly simple.

  1. First of all, make a paste of baking soda and distilled water.
  2. Once you’ve made the paste, apply it to the corroded areas and let them soak for 5 minutes.
  3. After the corroded areas have soaked for 5 minutes, you should then begin scrubbing at them with a wire brush.
  4. Once the corrosion has been removed, you should then tighten the terminals with a wrench.

After this, the issue should be fixed!


Here are some frequently asked questions that people have about their battery voltage decreasing while they’re driving!

Can Low Battery Voltage Cause Damage?

Yes, low battery voltage can cause damage to components in your car. For example, if the battery voltage is too low, then it can damage the starter in your car very quickly.

At What Voltage Should A Car Battery Be Replaced?

Generally speaking, a car battery should be replaced when it’s below 12.2 volts. If your car battery is reading lower than this, then you should try to charge it up to see if it will hold a charge. If it can’t then you’ll need to replace it.

Why Is My Batteries Voltage 12.5V While Driving?

If your battery voltage is at 12.5 volts while driving, then there’s no cause for concern just yet. It could just be that the car is already fully charged.

However, if you notice this consistently, or the voltage to continues to drop, then it could be a sign of a more serious problem.

Is It Normal For The Battery Gauge To Fluctuate?

Yes, it is normal for the battery gauge to fluctuate when you’re driving. This should not be cause for alarm as long as it doesn’t drop too low or stay at a low level for an extended period of time.


It can be worrying when you notice a decrease in your battery voltage while driving. However, there are a few possible causes for this such as an old car, faulty battery, old serpentine belt, corroded or loose terminals and more!

If you think that the cause is something minor like an old car or a corroded terminal then the fix should be relatively simple.

However, if the cause is something more serious like a faulty battery then you’ll unfortunately have to replace it.

If you are ever worried about your car’s battery voltage decreasing while driving, then make sure to consult a professional to help you identify and fix the issue!

Good luck!

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