How to Check the Voltage of a Car Battery

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There are few things more frustrating than discovering that your car won’t start because the battery is dead. A mechanic can measure the voltage in the battery, in order to determine whether it needs to be replaced. There are two ways to do this.

Open circuit voltage test

This car battery test determines how fully charged your battery is. This test is done twelve hours after shutting off your car, so that any surface charge can dissipate. This means a more accurate reading. The test is done with the engine off. Then your mechanic may either use a multimeter/voltmeter, or a dedicated battery tester. The dedicated tester is simply connected to the battery terminals and the voltage can be read. With the multimeter, the device is configured to measure voltage up to 20 volts. Then the leads are connected to the battery terminals, positive to positive and negative to negative to get the voltage.

A reading of 12.65-12.77 volts means your battery has a full charge. 12.45-12.54 volts means you have a 75% charge, 12.24-12.29 is 50% charged, and 11.99-12.06 volts is 25% charged. 11.75-11.89 volts means your battery is dead.

Electrolyte gravity voltage test

This is the method used for non-sealed lead acid batteries. With this method, a hydrometer measures battery voltage. A specific gravity of 1.269 means that the battery is fully charged. A reading of 1.229 indicates a 75% charge, 1.194 is a 50% charge, and 1.159 is 25% charged. 1.124 means you have a dead battery.

Performance and capacity load test

This type of car battery test measures the ability of the battery to produce current. Before you do this test, YourMechanic will test the car battery to be sure that it has at least a 75% charge. Then, the voltage of the battery is measured under a load similar to what it takes to start your car. Then, he or she will use a dedicated load tester – it’s a large resistor, with a resistance much like your car’s starter, and a meter that shows the output voltage – to apply a load equivalent to ½ of the cold cranking ampere rating of the battery for approximately 15 seconds. You should expect a reading no lower than 9.1 volts.

Have your car battery tested regularly. You should have your car battery tested at least once a year, preferably when the cold weather begins.


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Omar

10 years of experience
274 reviews
Omar
10 years of experience
Lexus ES330 - Battery - Boca Raton, Florida
I needed to help my 90-year-old mother with a new car battery, instead of her driving to a car repair, Omar came to her house with a new battery and properly installed it and was very kind and nice to my mom. I would highly recommend for any "at home" car repair needs.
Ford Mustang - Battery - Fort Lauderdale, Florida
Omar identified the trouble quickly and offered a solution. My car was fixed and ready for the road in no time.

Peter

23 years of experience
227 reviews
Peter
23 years of experience
Chrysler Sebring - Battery - Los Angeles, California
He said we had the wrong battery and my feathers fell. Looked lie he couldn't do it. Then I found that Peter went to a local parts shop and got the correct battery. I only took him about 30 minutes. Randell

Theodore

14 years of experience
1075 reviews
Theodore
14 years of experience
Toyota Prius - Battery - Bellevue, Washington
Theodore was absolutely phenomenal! I booked him to fix our company vehicle but was out sick the day he was scheduled to come. He was extremely patient as I coordinated for someone to let him into the parking garage. He fixed the car well and with efficiency and his communication was very very helpful. I would give more than 5 stars if I could. Than you Theodore.

Daniel

11 years of experience
4 reviews
Daniel
11 years of experience
Chevrolet Silverado 1500 - Battery - Riverside, California
5 stars all the way!! Knocked out the work quicker than expected and the price was cheaper than most shops.

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