Is Your Battery Voltage Dropping While Driving? – Solved with Free Tips


Is Your Battery Voltage Dropping While Driving

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It is always good and safe to have a sufficient charge in your car battery. Battery voltage dropping while driving can be a severe problem. You will be in a dilemma when the battery voltage changes while driving and you can’t find the reason.

The alternator is most probably not charging the car’s battery, which is why your battery voltage drops when accelerating. The alternator gives power to the car’s engine and charges the battery. Therefore, the battery will gradually lose power if it malfunctions.

There is much to learn about the causes of the dropping battery voltage in cars and how to fix it. Keep on reading to find out.  

How Many Volts Are in a Car Battery?

When fully charged and the engine is off, the car battery voltage range should be 12.4 to 12.8 volts on a voltmeter. This condition is called “resting voltage” since it is the normal car battery voltage. The battery will function at its peak within this range because it is in excellent condition.

The battery voltage will normally increase to 13.5 to 14.5 volts when the engine is on. In a way, it is good if the range is more than 12.9 volts since it indicates that the battery has too much voltage.

In reality, having more “juice” than the battery’s original requirement is not a negative thing. The built-in resistance makes it uncertain whether the battery is fully charged or not. To forcefully enter electricity into the battery, you must overwhelm it. You can give a voltage drop test to measure the current voltage issue in the car’s battery.

Typically, you need to raise a battery’s voltage to a minimum of 14 volts in order to charge it. Perhaps, the following standards may give some insight into recharging a car’s battery.

  • 100% battery charge at 12.6 volts.
  • 70% battery charge at 12.5 volts.
  • 50% battery charge at 12.3 volts.
  • 20% battery charge at 11.4 volts. 

Why Does My Car Battery Voltage Drop While Driving?

You need to find out why your battery voltage keeps going up and down while driving. Without wondering – “Why is my car battery voltage dropping?”, you should start determining the cause of your vehicle’s battery voltage fluctuations by using a voltage drop tester on several electronic parts. 

5 Reasons Why Battery Gauge Drops While Driving

You might be asking – “Can a bad battery cause voltage drop?” 

Well, of course, it does. Among many reasons, these are the most common ones for your car’s battery voltage dropping while driving –

#1 Malfunctioning Alternator

The alternator is the source of power for the car’s battery. Being an electrical generator, the alternator converts the engine’s mechanical energy into electrical energy. This way, it keeps the battery charged and supplies enough power to run the electrical components of the car. 

A malfunctioning or bad alternator can be the main reason for car battery voltage drops when connected to the engine. If the alternator goes bad or if it is overcharged, the entire electrical system of the vehicle won’t get sufficient energy from the battery.  


Typically, the alternator malfunctions because of its belt, which is known as aSerpentine Belt.” You need to change the serpentine belt when it is damaged or gets too old. It won’t cost a fortune to replace the serpentine belt.

Expert’s advice – You should change the alternator at least once every 7 years or when the mileage is over 80,000.

#2 Insecure Connections

Even if there is no problem with the alternator, your car’s battery voltage may still drop due to loose or insecure connections. Loose connections make it difficult for the battery to maintain the optimum voltage, which causes a drop in the battery’s voltage when driving. Moreover, the power supply on the battery and the alternator is impacted by faulty connections. 


You should look for sparks or corrosion around the connectors. After checking all the connections and discovering that faulty connections are the major cause of battery drops, you must replace all loose wires and reconnect them.

#3 The Vehicle Hasn’t Been Used for a Long

It is fairly common for your car to show negative symptoms, including a voltage drop in the battery if you leave it unused for a long time. Chances are high that the entire electronic system of the vehicle may not function at all. This is why the battery voltage drops while idling.


Take your car to the nearest mechanic’s shop and request that they perform a battery voltage drop test to see whether the battery is functioning or not. You can also run a voltage drop test by yourself with a voltmeter. The following video might help – 

#4 High Electricity Demand

The car’s battery voltage drops while driving if there is a lot of demand for power. When the electrical system is experiencing high current levels, the battery goes under a lot of strain, causing frequent voltage drops. 


You can prevent this by reducing the overall amount of electricity the system uses. At the same time, use a battery with sufficient capacity to manage the load. If you think the battery isn’t powerful enough to handle the electrical load, then it is time to change it.

#5 Battery Corrosion

When the battery gets too old, it is common to face corrosion. The battery gets damaged and can’t offer the maximum power for corrosion. As a result, the car’s voltage eventually drops while driving. 


Check the connecting wires between the battery and the alternator. If the wires are damaged or loose, the battery won’t provide sufficient power. Also, you should clean the battery from time to time. 

What Are the Signs of a Weak Battery?

A battery voltage low car is the result of a weak battery. You should change the battery when necessary. In fact, it is said that –

The average lifespan of a car’s battery is 2 to 3 years in the south and 4 to 6 years in the north.

There are symptoms that show your car’s battery is dying, and it should be replaced soon. Without further ado, let’s take a look at the bad battery symptoms.

Bad Battery Symptoms

You should take your car to a repair shop or troubleshoot the battery when you find the following symptoms 

  1. Cranking or Clicking Sound While Starting

You will hear a click or crank under the hood as soon as you turn the engine key. If you just hear a click sound, then it can be a failure at the start. But when you experience jump starts along with these sounds, then it is confirmed that something is wrong with the car battery.

  1. The car Won’t Start Easily

It is a common symptom of a bad car battery. Most of the time, the engine won’t start easily when there is a problem with the battery. A slow whirring noise will begin longer than normal before the car starts. You should definitely test your battery then.

  1. Dim Headlights

When the battery starts to fail, it won’t supply enough power to all the electronic components, along with the dim lights. When the headlights are dim for no reason, there is a high chance your battery is dying.  

  1. Backfire

Sparks that come and go might be caused by a dead automobile battery. Therefore, your car may often start to backfire. You can’t miss this particular cautionary notice. Backfiring might be an indication of several issues, so testing the battery is essential in this situation. 

  1. Jump Start

Batteries become less effective in storing charge over time. At that point, you will need frequent jump starts. Perhaps, it is time to buy a new battery if your existing one is not able to maintain its charge effectively.

Now that you are aware of the fixes when battery voltage drops while driving. Do you want to know how to test a battery isolator for your car?

Read How To Test A Battery Isolator with 5 easy steps.

FAQ – Battery Voltage Dropping While Driving

We came up with some of the most common questions that people ask, aside from the battery voltage drop issue. Let’s find out the answers to those questions.

What should the battery voltage be while driving?

A car battery should read 12.6 volts or more when fully charged. The appropriate reading should be between 13.7 and 14.7 volts when the engine is operating. If the voltage is above 14.7, the battery will be damaged quickly by excessive liquid coagulation. If the voltage is below 13.7, then your electrical components won’t function properly.  

Why does my battery voltage keep going down?

There are many reasons why your battery voltage keeps going down. A bad alternator, an old battery, a vehicle sitting idle for too long, excessive electrical load, or loose connections can cause your battery voltage to drop. Sometimes, the circuit restricts the functions of many electrical parts of the vehicle, causing a drop in battery voltage.

Is your battery voltage supposed to fluctuate while driving?

Yes, it is quite normal. The battery voltage fluctuates to maintain the charging state of the battery. If the charge is too low, the voltage rises to recharge it. When the battery is overcharged, the voltage drops slightly to prevent it.

How do I know if my alternator is draining my battery?

Open the car’s hood and start the engine to quickly check if the alternator is sucking the life out of your battery. Disconnect the negative battery wire when the vehicle is still running. The alternator is most likely defective if the car stops or dies.

How do you fix a low voltage car battery?

You can fix a low voltage car battery easily by taking the following actions –

-Take out the battery from the car and recharge it.
– Fix or replace the alternator.
– Jumpstart the car.
– Change the battery if required.

Most of the time, a jumpstart should fix a low voltage car battery. However, you may need to change either the alternator or the battery itself for major issues. 

Have You Prevented Battery Voltage from Dropping While Driving?

In summary, if you notice the voltage of your car’s battery is between 12.4 and 12.6 while it is idle, then you can assume it is in decent condition. And the range should be between 14 and 14.6 volts when your car is running. 

Also, remember, before you finally change the car’s battery, you should try removing rust, if there is any, and cleaning the terminal properly. To make sure battery voltage drop issues never arise again, you should not keep your car idle for a while. You should take your car out occasionally for a test drive. 

About the author

One response to “Is Your Battery Voltage Dropping While Driving? – Solved with Free Tips”

  1. Michael Palmer Avatar
    Michael Palmer

    My 2007 Tahoe battery is new alternator is new but after I drive around 5 miles the gauge drops to 13 it should be 14. So I come home cut it off and try to start again and it won’t start.i let it sit for a while and it started.

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