An automotive battery should measure at 12.6 volts when fully charged. A battery is only twenty-five percent charged at 12 volts and is considered “dead” when it falls below 11.9 volts. One way that a technician will test a battery is to use a voltmeter to measure how much voltage is present.
At one time, car batteries (which contain an electrolyte solution of sulfuric acid and water) had removable caps that would allow a technician to service the battery. The technician would remove the caps and test the electrolyte solution to determine the battery’s condition. Today, most batteries are “sealed”, so that test is rarely possible.
Another battery test is a “load test” that measures its ability to produce current. A device is employed to produce a load on the battery (using a large resistor) and to simulate the draw of a car starter. A meter on the device shows the output voltage under the load.
During a battery test service, you can expect that a technician will do the following:
Many drivers have experienced a dead car battery. You get in the car, turn the key in the ignition, and hear nothing but a constant clicking sound. Or maybe the engine turns over slowly but refuses to start. Leaving the dome light on overnight or the stereo on for too long at a picnic can drain your battery too low to start the engine. A jumpstart or battery charger can often remedy the problem.
If you find that you are needing frequent jumpstarts or charges, on the other hand, your battery might need to be replaced. But before you spend the money on a new battery, a technician can test the old battery to see if there is life left in it, or if there is some other issue (such as a bad alternator) that is causing the dead battery. Other conditions that might indicate that a battery test service should be scheduled include:
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