Most people know that the battery in their car has a 12-volt rating, but what voltage is a car battery really? It might surprise you to learn this value isn’t stable over the life of the battery. Knowing your battery’s voltage is important in identifying and repairing issues.
If your car isn’t starting consistently (or dying often), you might have a low voltage. Let’s look at what this means and how to make an accurate diagnosis so you can get back on the road.
What Is Car Battery Voltage?
The voltage of a battery is a measure of its potential stored energy. Specifically, it measures the difference between the potential of the positive and negative battery terminals.
Batteries generate electricity by passing a charge from one terminal to the other. The negative terminal has an excess of electrons, which are negatively-charged particles. These particles want to travel to the positive terminal, which has a corresponding lack of electrons.
When your battery is off, these electrons are prevented from traveling from one terminal to another. Once it’s activated, a circuit is formed between the terminals. The flow of electrons is what provides the energy that powers your vehicle’s electronic components.
You can measure the rate of electron movement in amps. A battery’s ampere-hour (or aH) rating tells you how quickly the electrons move from the negative to the positive terminal. The more electron movement, the more energy is provided.
How to Check Car Battery Voltage
The easiest way to check your car battery voltage is with a multimeter. These are handheld devices that can check devices for various types of electrical currents. To use a multimeter to test the battery voltage, follow the steps below.
- If you’ve recently been driving your car, let it sit for at least an hour (overnight is better, if you have the time). The charging system in your engine refills the battery with energy. Testing right after driving will give you a false high reading because of this. You’re looking for the battery’s “resting voltage,” or the potential in the battery when it’s cold and out of use.
- Set the multimeter to DC voltage, with the dial at 20.
- Touch the red probe of the multimeter to the positive terminal. This will often be red and marked with a plus (+) sign.
- Touch the black probe to the negative battery terminal. This is typically black and will be marked with a minus (-) sign.
- The voltage measurement should be displayed on the multimeter’s window. If you see a negative reading (e.g. -12.6), you have the probes on the wrong terminals and need to swap them.
- If you get a reading that’s lower than 12.6 volts, disconnect your battery from your vehicle and charge it with a battery charger. Batteries in modern cars with electronic systems often experience what’s known as “parasitic loss.” This is when something like the clock, radio, or lights uses up the power when the engine isn’t on to recharge it. Testing the battery after a full charge tells you if the battery is the problem, or if there’s something else in your system draining too much power.
Often the cells in a battery don’t die all at once. Individual cells can be tested with a device known as a hydrometer to identify the culprit. Unfortunately, most modern batteries are sealed and don’t allow access to the individual cells. If this is the case, you’ll need to replace the entire battery if it’s reading below 10 volts.
Car Battery Voltage Chart/Range
A lot of people think a discharged battery has a measure of 0 volts, but that’s typically not the case. In fact, the voltage measurement between a healthy and dead battery is much narrower than this, as you can see from the chart below:
|% of Charge Remaining
You should be able to start your car with no problem with a reading of 11.9 and above (though your battery could still use a charge). Once you get below that, though, you’re likely to experience issues and may need a jump to get started.
What Voltage Should a Car Battery Be?
So if your car battery is 12 volts, that’s it’s energy potential, right? Well, not exactly. The 12-volt rating is an approximate measure of a battery’s potential when it’s off.
When fully charged, a car battery should measure at least 12.6 volts. This number can go up to around 13.7-14.7 volts when the car is running.
As a battery age, its potential energy naturally drops as the plates inside wear out. It requires about 10 volts to start an engine, so once your battery drops below that it is functionally dead.
Why the Voltage of a Car Battery is Important
Knowing the voltage of your car’s battery lets you know its underlying condition. An old battery with a low voltage will be more likely to fail on you when you need it. This leads to stalling and may send you looking for a jump.
In addition, the battery does more than just start your car. It’s also what powers electrical systems, including the lights, automatic windows, radio, and other components. Knowing that your car battery has a good voltage can give you confidence these features will keep working.
The Bottom Line
Knowing how much voltage is left in your battery is a key step in diagnosing electrical problems. By measuring it cold and outside the vehicle, you can easily identify if you have a dying battery or if there’s something else in your car draining its power.
If your car battery is reading below 11.9 volts, that doesn’t necessarily mean you have to replace it. A car battery charger with a desulfation function can restore the plates inside to their original glory. This can help you get more use out of your battery, saving you money in the long run.
The bottom line is that understanding your car battery voltage helps you identify when it needs to be replaced. We hope the breakdown above has given you the knowledge you need to diagnose battery issues successfully!