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How Many Volts Is a Car Battery?

Jumper cables attached to a car battery

A car battery serves as your vehicle’s nerve center. When it’s working properly, it supplies electricity to the ignition to activate the engine, heats and cools the car, and enables multiple accessories to operate, including the infotainment center and navigation. On the other hand, a dead battery means you’re not going anywhere. One way you can gauge your battery’s health before you get stuck with a dead battery is to measure its volts. Here’s an in-depth look at car voltage and battery health.

How Many Volts Is a Car Battery?

Voltage represents motivation, or the way electrons are moved from one point in the circuit to the other. How many volts is a car battery? Well, batteries can support a range of voltage, depending on their age and condition. Car batteries are usually labeled as 12 volts, but they hold closer to 15 volts thanks to the power they receive from the alternator. In fact, a battery’s voltage should register nearer to the higher range if it’s working properly, but different numbers may be recorded under varying conditions.

When your car is running, your battery should register between 13.7 and 14.7 volts. If it reads 12.4 volts, this means the battery is operating at only 75 percent capacity. It’ll still get the job done, but the lower number serves as a warning that either the car battery isn’t getting enough power or it has aged and will soon require replacement. Battery power drops sharply after that — a reading of 12.2 volts signals 50 percent power and 12 volts registers just 25 percent. If it reaches 11.9 volts, the battery is considered fully discharged.

voltmeter DVM

How to Test Your Car Battery’s Voltage

A voltmeter is useful for measuring voltage, and it’s easy to use. Just connect the positive end of the voltmeter to the battery’s positive terminal, and connect the negative end to the negative terminal. In addition to gauging the battery’s strength while the car is running, you’ll also want to test its performance under load — when you’re starting your car. The connected voltmeter will register a lower number, which reflects the amount of power available to start the car:

Set the connected voltmeter to above 10 volts. Have someone start the car while you observe the meter. The number should begin to drop as the vehicle cranks. As long as it doesn’t fall below 9.6 volts, you have sufficient cranking power. If it falls below that, then you’ll need to replace the battery. Otherwise, the meter reading should start rising as the alternator recharges the battery. Within 20 seconds you’ll have both the load test readout (the low score) and the normal reading (the high score). Together, both scores serve as good indicators of battery health.

When to Replace Your Car Battery

While a low meter reading is a strong indicator of battery distress, a drained battery — perhaps the result of lights being left on for several hours after turning your vehicle off — could lower the readout as well. Moreover, if you’re running many accessories at the same time, that will drain the battery as well.

To remedy a weak battery, simply run cables from the distressed battery to a strong one. Keep the batteries connected for a few minutes to ensure enough power is transferred, and then use the voltmeter to gauge the battery’s strength. If it remains weak, then it may be time to replace your car battery.

Check out all the batteries available on NAPA Online or trust one of our 17,000 NAPA AutoCare locations for routine maintenance and repairs. For more information on car batteries, chat with a knowledgeable expert at your local NAPA AUTO PARTS store.

Photo courtesy of Pixabay.

Matthew C. Keegan View All

Matt Keegan has maintained his love for cars ever since his father taught him kicking tires can be one way to uncover a problem with a vehicle’s suspension system. He since moved on to learn a few things about coefficient of drag, G-forces, toe-heel shifting, and how to work the crazy infotainment system in some random weekly driver. Matt is a member of the Washington Automotive Press Association and is a contributor to various print and online media sources.

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