How to Check the Voltage of a Car Battery

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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Keven

7 years of experience
118 reviews
Keven
7 years of experience
Ford Explorer V8-4.6L - Battery - Spanaway, Washington
Since we have started using YourMechanic and Kevin has been our mechanic we have gotten nothing but the best service. He always goes above and beyond and gives his best to insure we are taken care of.
Kia Soul - Battery - Puyallup, Washington
Kevin, is wonderful. He is on time and very efficient. He explains things very well and answered all my questions. Very friendly too. I would highly recommend Keven and plan on using him again if mechanic service is needed.

Carlos

28 years of experience
501 reviews
Carlos
28 years of experience
Jeep Compass L4-2.4L - Battery - Santa Ana, California
Carlos went above and beyond during the appointment, and was incredibly patient and kind when chatting with me about the car. His knowledge and professionalism was impressive and I'm very happy with the appointment.
BMW 750Li xDrive - Battery - Mission Viejo, California
He was behind schedule but let us know right away and as soon as he arrived he got the work done extremely fast. He is also very knowledgeable and informative. He was courteous and friendly. My husband and I would use him again with confidence.

Brian

7 years of experience
32 reviews
Brian
7 years of experience
Saturn Vue V6-3.5L - Battery - Dayton, Ohio
Brian was awesome he communicated with me through out the process and was a joy. Service was lengthy (car had a lot to fix) but completed well I will definitely use him again
Honda Accord - Car Battery Replacement - Dayton, Ohio
An expert at his craft. Fast with his work without missing a detail. Very personable. Highly recommend.

Jamie

22 years of experience
91 reviews
Jamie
22 years of experience
Toyota Corolla L4-1.8L - Battery - San Bernardino, California
This was the fastest car service I have ever had. Switched out my battery and check other things with my car and was done before I knew it. Will definitely continue to use this for more car maintenance.
Chevrolet Equinox - Battery - San Bernardino, California
Very friendly and knowledgeable. Great personality. When I need you again I will surely ask for him. Thanks Jamie.

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