Why Is Your Car Battery Voltage Too High? – Ask The Expert

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It’s the heart of your car and one problem relating to it can prevent you from going anywhere.

 It’s your car’s battery.
As with any human organ, this is a part you can’t simply leave until it stops functioning.

Checking it and maintaining it will ensure it lasts you as long as possible and the rest of your engine won’t be damaged by its malfunctioning. 

Maintenance can even prolong its life cycle.
But what if you notice a problem? If your car battery voltage is too high you need to tend to it directly. And we will show you how.

Is high voltage a big problem?

Why is this an important part of your vehicle maintenance? Is too much power in a car really a bad thing? It is if you want your car to last long.

The reason the power is regulated is that too much of it will cause risks:

  • Voltage will become dangerously high
  • The battery can overcharge which will leave it useless
  • Engine components that aren’t designed to handle the pressure, temperature or power will be damaged
  • The alternator isn’t designed to handle excessive power and eventually it will burn out

This can happen without you knowing. Your first clue may be when your car cuts out or doesn’t want to start anymore. This is why regular maintenance is essential.

General Guidelines – What To Check For

How do you know if your battery is giving problems?

These days maintenance is fast and easy. You don’t even have to visit a professional mechanic. An ordinary volt meter or power probe can be used to test your battery. Simply make sure the battery wasn’t charged recently so you get accurate readings.

12V batteries. Your reading should be anything between 10V and 12.9V. An ideal reading is between 12.4V and 12.7V. Some experts say a reading above 12.6V is better. As soon as your engine is switched on it should increase to 13.7—14.7V.

If it reads below 10V, your battery is going to die very soon. When it rises above 12.9V—while your car isn’t switched on—you have a problem. This can turn into a hazard for you or your car, so you need to find the problem and repair it.

No, it’s not necessarily your battery. Many engine parts connect to the battery and the source of the problem can be there.

what to check

Reasons why voltage peaks

Loose connections

A simple problem of loose wires and connections can cause your battery voltage to fluctuate. You may think it is flat, charge it and afterwards voltage can go as high as 15V or 16V.

Here are a few connections to check:

  • The starter solenoid
  • Corrosion on all wires leading to and from the alternator and battery

If you have tools and skills, you can repair these yourself or ask a professional to play it safe

Alternator problems

Inside your alternator is a voltage regulator. This part manages your battery’s voltage. If it malfunctions you experience fluctuating voltage readings.

Luckily you don’t have to replace either the battery or the entire alternator. Alternators can be repaired. There is a quick solution and most professionals can repair the unit while you wait.

The starter

Since your starter has a direct connection to your alternator, you may want to check this part too. Even if your connections are sound, the part itself may be damaged. If it’s already showing signs of wear and tear, it’s best to replace it.

Your car’s starter impacts the battery. A problem in the starter can lead to problems in the other parts leading to the battery’s working, such as the alternator.

Do you struggle turning your key in the starter unit? Remember that continuous use of damaged or substandard parts can create huge problems in your engine over time. The moment you realize a part gives problems it’s wise to repair or replace it.

The battery itself

Firstly, realize the hazard of working on a battery; a car’s battery has the capacity to cause you harm. Safety procedures are of the essence.

You can test a battery in its normal condition, without the car being switched on. You’ve found the source of the problem if your readings are outside these guidelines:

  • Minimum 12.4V
  • Maximum 12.9V

There’s little chance of repairing a battery and adding liquid won’t necessarily help. In this case you’ll have to purchase a new one.
Does a hopeless feeling come over you when your car shows signs of trouble? ​

If it’s your battery there are only a few parts you can check for the source of the problem. 


Now you know where to look and you can take necessary action... When did you last check yours?

Last Updated on 10/01/2021

11 thoughts on “Why Is Your Car Battery Voltage Too High? – Ask The Expert”

  1. My car 2009 z06 shows “battery voltage high”it reads 16v – 16.9 when I “lug” the engine starting off it will drop down to 14.7 – 15.3 new red top battery replaced alt checked all connections I could find. Your opinion is that I should change the starter out the has 15,500miles would apreaciate any help you can give thanks I would like to give your article a favorable rating

  2. I have a 99 Ford explorer. I had a battery that went dead and I put another battery in it was not a new battery but I charged it and it held a charge it was just one I had laying around the garage. When I started the truck up the truck battery gauge went all the way up to the h. So I turn the truck off and went and got my volt meter. Testing the battery for voltage with the truck off the battery voltage was at 12.8 roughly. Then I started the truck again and with the truck running it was reading 24.5-26.5. I never had a voltage problem before I change the battery. The alternator is less than a year old I bought it from O’Reilly’s and it is a new alternator not a rebuilt one. Looking for some clues to do at home diagnostic to see if I can’t figure out what’s wrong I need some help as anyone have any ideas. I took the battery out of the truck I’m currently have it parked because I’m scared the battery is going to blow up or start a fire or kill all the electronics in my car running voltage that high. Thank you in advance for any help or advice that I may get from you guys.

    • i having the same problem reading 26 volts did you ever find out why i need a answer my self helpppppppppppppppp

  3. I have 15.5 voltage reading at the battery terminals now. car running. Measuring with a professional meter. Measured volt output coming out of the alternator 12.7 volts , car running. Makes no sense to me. I would think since there would be higher volt reading from the alternator.. the car is a 1970 Monte Carlo and has a separated voltage regulator. 3 wire alt. not sure what amps to read from the regulator going into alternator vice/ versa Thinking about replacing both alt and reg. Does this make sense or should I check further. Professional opinions are appreciated. I’m not so good at trouble shooting auto charging paths

  4. My 2009 cadillac cts won’t start it has never done that, but it say the battery voltage over time, what’s that mean n

  5. Good day my battery read 18v when the car is switched off, what could be the problem?

  6. I have a 2012 gmc arcadia Denali my problem is the my battery voltage runs atabout 15.5 and even running the engine for awhile the voltage will not drop down to 13 is that a indication that i need anew alternator or new battery

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