Overview of Battery Diagnostic Technologies

There are a wide range of battery test methods, and not all of the methods are discussed here.  

Voltage testing
Specific gravity
Load testing
Discharge testing
AC conductance testing
Crank effort testing
Large Pulse Resistance testing

For additional information about battery testing, download the Guide to Battery Testing Technologies. (Requires Acrobat Reader.)

Voltage Testing

Measuring battery voltage is inexpensive and very easy with any basic voltmeter. However it is a very crude method of evaluating a battery. Voltage alone can be used only to understand how charged a battery is. Voltage measurements can't be used to indicate battery capacity, capability, state of health, or battery life.

Specific Gravity

Using a simple gravity tester, electrolyte can be withdrawn from batteries with removable cell covers. The specific gravity can indicate charge level and the need to add water to the battery. However, as with the voltage measurement method, little information about battery capacity, capability, state of health, or battery life can be determined from a specific gravity test. Additionally, many batteries made today are permanently sealed and it is not possible to extract any electrolyte for testing.

Load Testing

A basic load test uses a volt meter, a load element, and a switch. Activating the switch connects a fixed load to the battery. A typical load for an automotive battery is approximately 60 to 100 amps. If the voltage of the battery falls below a specific threshold within a period of time (typically 30 seconds) the battery is considered to have failed.

This method of testing can be used to identify batteries that have decayed beyond their useful life. However, this method can't be used to indicate battery capacity, capability, state of health, or battery life remaining. Importantly, for this method to offer any useful results, the battery must be fully charged prior to testing, be at a normal temperature, and the test load and test duration must be carefully matched to the battery size. Finally, this method causes significant discharge and stress to the battery.

AC conductance testing

AC conductance testers apply a small AC signal to the battery and measure the oscillating voltage response. The resulting AC conductance of the battery can be measured. This conductance value can be converted to a value representing battery capability and compared to the original rating of the battery by the manufacturer. Using this method the general capability of the battery can be established and state of health can be estimated by understanding how much capability has been lost compared to the battery manufacturers rating.

Crank effort testing

Crank effort testing is one exception to the general rule that "you get what you pay for." All other methods discussed above provide a measure of battery condition relative to a standard such as 'full' or 'new'. While these comparisons are useful, they offer little direct information about how the battery is able to perform a specific job. The crank effort testing method is designed specifically for batteries used in engine starting applications. By measuring the effort required by the battery to crank the engine, the battery's cranking health can be determined and plotted along a scale of 0 to 100. This result is the most direct and useful indication of performance because it is based purely on the battery and its demonstrated ability to perform the specific task it is needed to perform. 

For a more detailed description of Crank effort testing, please read about CrankCheck.

Large Pulse Resistance (LPR) testing

LPR testers apply a large load for a very short period of time. The DC resistance of the battery can be calculated from the voltage measured while the load is turned on. The DC resistance can be converted to battery capability and compared to the specification of the manufacturer, resulting in a measurement of battery life or state of health. The large load applied using LPR testing exposes a range of battery defects not detectible with small signal test methods. When used in combination with voltage testing, and crank effort testing, LPR provides a comprehensive picture of battery capability, charge level, and state of health. Read more about LPR here.

The Argus AA350 uses the LPR test method, while models AA400, AA500P, and AA500PWP (tester/printer kit) use both LPR and Crank effort testing.