How to Check the Voltage of a Car Battery | YourMechanic Advice

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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YourMechanic Car Battery Replacement Service

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Number of Reviews

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Rating Summary
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6,207
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Behrak

8 years of experience
111 reviews
Behrak
8 years of experience
Jeep Cherokee - Battery - Atlanta, Georgia
He went above & beyond to ensure that the battery needed to be changed before just jumping to change it.
Ford Escape - Battery - Alpharetta, Georgia
Behrak was on time (actually he was early, and checked with. me first to make sure that was okay), did the job very quickly but thoroughly, and answered every question I had. Highly recommend him and his services.

Jason

14 years of experience
228 reviews
Jason
14 years of experience
Audi A4 Quattro - Battery - Bronx, New York
He came an entire hour early to my second booked Battery replacement appointment after I cancelled my first one with him. He came with the correct sized battery, changed it quickly & ran a good accurate inspection. Good professional.
Toyota RAV4 - Battery - Long Island City, New York
Was able to push up my appointment for a day earlier which was very helpful. Was professional and efficient with his repair.

Pierre

8 years of experience
117 reviews
Pierre
8 years of experience
Mazda 3 - Battery - Brookline, Massachusetts
Pierre was on time, accurate with his assessment & repair, helpful in explaining what the issues were and was generally great to talk to!
Ford Explorer - Battery - Wellesley Hills, Massachusetts
very good experience. Pierre was on time, did a great job diagnosing the issue, and was highly professional.

Shawn

11 years of experience
94 reviews
Shawn
11 years of experience
Lexus ES350 - Car Battery Replacement - Wayne, Pennsylvania
Shawn was friendly, knowledgeable, and very quick! 30 minutes and car battery was replaced. Thank you Shawn.
Lincoln Continental - Battery - Lancaster, Pennsylvania
Shawn was very helpful and professional. He found that the problem wasn’t the starter, but the battery. I would use the service again and recommend it to others.

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