How Do Load Testers Work?


Quick Answer

Battery load testers work by connecting to each of the battery's poles and passing the electrical current from the battery through a conductive material inside the load tester. A sensor connected to the conductive medium inside the load tester responds to the change in current, and it moves a needle on a gauge that the operator uses to determine the amount of voltage still present in the battery.

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Full Answer

While battery testers provide a useful measurement of a car battery's total available current, the actual readings they produce are nearly always inaccurate. This happens because lead-acid cells used in manufacturing car batteries do not function or deteriorate in the same way that alkaline batteries used in small devices do. When an alkaline battery deteriorates, it does so in a uniform fashion. However, when a lead acid battery deteriorates, its current does not wear down uniformly or evenly.

Battery load testers are also useless for testing battery capacity. In fact, no tester exists that can reliably measure a lead-acid battery's capacity. This inability to determine capacity sometimes causes problems, because a vehicle may produce sufficient voltage to give a good reading on a load tester, but not be consistently able to produce that voltage once on the road. This same problem can cause good batteries to be thrown out prematurely, as a battery with low current but high capacity functions perfectly well after recharging.

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