What You Need to Know About Car Battery Voltage
Batteries are one of the most important parts of your car. They may not be the newest technology or cost the most, but without a battery, you won’t be able to turn on your car, and you’ll be left stranded.
Car batteries are responsible for powering the electrical elements of your vehicle when the car is turned off, such as the lights and the stereo. But more importantly, they provide the power to crank your engine and start your car when you turn the key.
An important element of any battery, whether it’s for your car or your TV remote, is the voltage. Here’s everything you need to know about voltage in a car battery.
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What is Voltage?
In layman’s terms, voltage is the pressure from a power source that pushes current (charged electrons) through a conducting loop, which allows them to do work. Or, to put it even more simply, voltage is the amount of electrical potential that a battery has.
This is important in cars, because a certain amount of voltage is required to turn on your vehicle. There’s a reason that your vehicle relies on a large, bulky battery under the hood and not some tiny AAA batteries. In order to start, your car needs more power than a small battery can provide, and that power is displayed by voltage.
How Much Voltage Does Your Car Battery Have?
Standard car batteries are listed as 12-volt batteries. However, this is rounding down, as a car battery should have a “resting voltage” – which is to say, the amount of voltage it has when it’s turned off – of 12.6 volts. That voltage increases when the car is running. Once your vehicle is up and running, the alternator powers the electrical elements in the vehicle, like the lights, stereo, power windows, and power seats. The alternator is also responsible for charging the battery, so that it’s fully prepared for the next time you turn on your car. With all that extra electrical current from the alternator, a car’s battery usually has a voltage of 13.5 to 14.5 when running.
How Much Voltage Does a Car Battery Need?
A battery needs the bulk of its voltage in order to function properly. While some people think that a battery has to get down to zero volts before it stops working, the reality is that a car battery can’t dip too far below 12 volts before it’s unable to perform its duties and turn your vehicle on.
Here’s a car battery voltage chart that correlates a battery’s voltage to its life, to help display how many volts are really needed to keep your car running happily.
| Voltage | State of the Battery’s Charge |
| 12.6 or higher | 100% |
| 12.5 | 90% |
| 12.42 | 80% |
| 12.32 | 70% |
| 12.2 | 60% |
| 12.06 | 50% |
| 11.9 | 40% |
| 11.75 | 30% |
| 11.58 | 20% |
| 11.31 | 10% |
| 10.5 or lower | Dead |
How to Test Your Car’s Voltage
While you can always take your car to a mechanic (or an oil change spot) to have the voltage checked, it’s an easy task to do at home. All you’ll need is a multimeter or a voltmeter, both of which are quite affordable.
Start by turning the car off, and removing the battery’s positive terminal cover. At this point, it’s a smart idea to check the battery’s terminal for corrosion and clean off any that you spot. Next, attach the positive lead of the multimeter or voltmeter to the positive lead of the battery, and then attach the negative lead of the multimeter or voltmeter to the negative lead of the battery.
Now you’ll want to turn the key of the car to the run position, and get a reading on the multimeter or voltmeter. This will tell you the car’s voltage. It should be sitting between 12.6 and 12.8, though it can be a little bit lower depending on the weather. If the voltage is above 12.8, you should drain the battery a little bit by using the electrical components before turning it on. If the voltage reads below 12.6, you probably need to charge your battery.
What Causes a Battery to Lose Voltage?
The primary reason that a battery loses voltage is time and use. Since voltage is a current, it doesn’t get used up when you use your battery, the way your car uses up gas. However, the frequent generation of power results in the battery’s chemicals slowly turning into different chemicals. Those chemicals are less capable of providing power, and the voltage in the car’s battery will begin to drop.
Most lead-acid batteries need to be replaced every three to five years, because sooner or later the voltage will start to run dry. If you have an EFB or AGM battery, its lifespan might stretch by an extra year or two.
What Are the Signs of a Weak Battery?
While you can use multimeters and voltmeters to determine the voltage in your car’s battery, your car will also usually give you a fair amount of warning signs when the voltage is beginning to dwindle, and the battery is starting to go.
You might notice some electrical issues with the car, such as headlights that are too dim, or flickering, or power windows that are moving more slowly than usual, or poor sound quality from the stereo. Sometimes those electrical components simply won’t work at all if the battery is fading.
But the most sure sign of a weak battery is trouble starting your car. If the vehicle won’t turn on, that’s usually a sign of a battery that is dead or dying. If the car will turn on, but it takes a few tries or starts on a delay, then the battery is probably fairly weak.
Whether you need to buy a new battery, a multimeter, a voltmeter, or the tools to work on your car, you can find whatever you’re looking for at AutoZone. You’ll get the quality of the top brands, and the convenience of Same-Day In-Store or Curbside Pickup, as well as Free Next-Day Delivery on eligible orders. If the job is too big for you, seek out one of our Preferred Shops to help you do the job.
