Battery tester can detect the capacity and voltage of battery during discharge, it displays by scales,so that we can know whether the battery is in a normal state, or needs to be charged, or need to be replaced. Operating voltage: 12V Capacity: 100A Test range: 20Ah-200Ah Product size: 305 * 152 *72MM Instructions for use: 1.put two clips on the positive and negative poles of tester , then lights on (clip ends is positive side), voltage meter indicates battery voltage, this time for virtual voltage (load voltage). 2. Does not light or voltmeter pointer does not move, check the battery pole clamps and good contact. 3. Twist toggle switch, do not more than five seconds, the battery rated capacity of 3 -500Ann, the discharge current is 100-120. (At this point the tester to the battery discharge to 100A), offset voltage meter pointer to the left, according to the offset position to judge the condition of the battery charge. a. pointer in the Green Zone, said fully charged. b. pointer in the yellow zone and low battery indicator is steady, need to be recharged. c. pointer down the left quickly, indicating that the battery has not kept electricity. d. pointer back to zero, indicating that the battery may break grid. e. pointer in the red zone, said the battery power is low, the battery may be defective.