3.7V uses a red power , 4 (the other is 1 red power , 4 ) Ultra-thin Electricity display, 5 LED indicators, display more and more beautiful. the positive and of the display board and it to the positive and ends of the battery to be tested. Lightly press the red button with your finger and the lamp lights up to show the real-time battery power. Loosen your finger and the LED light will be extinguished after 3-5 seconds of delay. power will be consumed during . 3.7V , full 4.2V.