The MODEL 42 contains an integral high power resistor load bank which is switched across the battery via a high power contactor. The contactor is operated from the control electronics allowing the load to be applied and removed in accordance with the automatic test sequence, this ensures no power is drawn from the battery when the croc clip leads are first connected.

Before beginning a test, the user sets the size of the battery being tested on a front panel control, this automatically sets the internal calibration of the tester to match this battery size.

The test sequence begins when the START push-button is pressed, this closes the contactor applying the 100A load to the battery for 5 seconds (to remove any surface charge that may remain from the last re-charge). If the battery voltage falls rapidly, as may be experienced with a flat or faulty battery the load is automatically removed. At the end of the 5 second load period the battery is rested for a further 15 seconds, this allows the battery voltage to recover as the open circuit voltage is sampled to check the battery charge level. The charge level is then displayed on a 5 bar yellow led display in 20% increments.

At the end of the first 20 seconds, the battery is load tested again to establish the batteries condition. The on load voltages measured during the on load test sequence are compared with the internal calibration settings and the test result is displayed on a coloured LED display. (See testing a battery)