How Do I Find the Voltage of My Car Battery?

Car batteries generate the short burst of electricity needed to turn over your engine. Over time though, your battery becomes less efficient at holding a charge, which is why you should occasionally test its voltage to make sure your battery is performing properly. Today we’ll walk you through how much voltage your battery should have and how to test it using a multimeter.

How Many Volts Should a 12-Volt Battery Have?

A 12-volt battery is standard in most modern vehicles. It consists of six cells, each of which contains 2.1 volts of power at full charge. Therefore, a car battery is considered fully charged at 12.6 volts or higher when the engine is off. When you start your car, your battery’s voltage will drop for a short time before climbing back up to its running voltage. During the starting process, a healthy car battery should have a voltage of 10V or higher (although this can be lower in instances of cold weather). Once the vehicle is running, this measurement will be slightly higher. This is because your alternator is actively charging your battery. With the engine running, your battery’s voltage should be somewhere between 13.5 and 14.7 volts.

What is the Minimum Voltage Needed to Start a Car?

When your battery’s voltage drops even a small amount, it makes a big difference in its overall performance. The chart above shows what the voltage should be for different states of charge. As you can see, a voltage of 12.1V means your battery is operating at only 50% of its total charge. If your battery drops to a voltage of 11.9V or less, you’re going to notice a serious drop-off in performance. Once it goes down to 11.6V, the battery is almost completely discharged.

How Many Volts Should a Car Battery Lose Overnight?

It’s normal for your car to lose a small amount of charge each night due to parasitic draw. Parasitic draw refers to anything that continues to draw current from the battery after the engine is shut off. Examples of this include your car’s interior lighting, clock, the settings on your car radio and its alarm system.

Fortunately, the amount of current drawn from these applications is minimal. For newer cars, you can expect between 50 and 80 milliamps of power, which works out to 0.05-0.08 volts of power. Older cars tend to have less interior electronics and will typically draw even less than 50-milliamps of power over the course of a single night. If you have a car that you don’t use very often, you need to be proactive in keeping the battery charged. For a list of suggestions, read our blog titled "How Do You Keep a Car Battery from Dying When Not in Use?"

What are Some Other Factors That Affect Battery Voltage?

In addition to parasitic draw, there are a number of additional factors that can impact your battery’s performance and lower its voltage. Read about six things that can drain your battery and find out what you can do to help prevent them.

How Do You Measure Your Car Battery’s Voltage?

You can measure your battery’s voltage using a handheld tool called a multimeter. Just follow these simple steps.

1. Switch off any additional power draws, including headlights, sidelights, radio, air conditioning, GPS, etc.
2. Conduct your test after the car has been sitting with the engine turned off for a period of time.
3. Make sure you’re using the proper safety gear; eye goggles & sturdy, waterproof gloves
4. Set the multimeter to voltage, then adjust it to somewhere between 15 and 20 volts of DC (direct current) power. If your multimeter doesn’t have incremental settings, just set it to DC volts.
5. Double-check that the vehicle’s ignition is off, then remove the cover from the battery
6. Wipe any grease or corrosion from both of the terminals to ensure a good electrical contact
7. Connect the multimeter to the two terminals, with the red lead touching the positive terminal and the black lead touching the negative terminal.

How to Interpret Your Multimeter Reading

If your battery has a charge between 12.4V and 12.7V, your battery is fully charged and ready to run. If your voltage is below 12.2V, it needs to be recharged. Take a 30-minute drive on the highway or pick up a charger to bring the voltage back up. If your voltage is higher than 12.9V, the battery is overcharged. Overcharging can damage a battery, so you’ll want to remove some of that excess current. You can do this by switching your headlights on the high beam setting for a short time and then testing your battery again to make sure it’s in the ideal range.

Batteries Plus Tests Vehicles Batteries for Free

Of course, if you don’t have a multimeter, you can always bring your vehicle to your neighborhood Batteries Plus. Our experts will be happy to test your battery for you, free of charge. We also install new car batteries on most vehicle makes and models. You can even cut down on your wait time, by scheduling your arrival time online.

Do you live in an area prone to extreme temperatures? Learn how to find the best jumper cables or how to jump start a dead vehicle using a portable power pack. Then, visit our Automotive Center for a huge selection of headlight bulbs, auto fuses, wiper blades and more.