This product is a voltage controller, which turns on and off the output through a relay, which only acts as a switch and cannot change the voltage. Charging mode IN: By setting the upper limit voltage UP and the lower limit voltage ; when the battery voltage less than or equal to the lower limit voltage , the relay is turned on, and the charger starts to charge the battery; when the battery voltage greater or equal to the upper limit voltage UP, the relay is disconnected to complete an automatic charging; the relay is turned on, IN flashes, indicating that it is charging. Discharge mode OUT: By setting the upper limit voltage UP and the lower limit voltage ; when the battery voltage greater or equal to the upper limit voltage UP, the relay is turned on and starts to discharge; when the battery voltage less than or equal to the lower limit voltage , the relay is disconnected to complete an automatic discharge function; the relay is turned on and OUT flashes, Indicates that it is discharging. Note: This product is a simple voltage controller, which uses a relay to turn on and off the output. It only functions as a switch and cannot be formed. Function: Calculation of voltage percentage: battery voltage/(upper limit voltage-lower limit voltage) Button: UP button: Short to switch to display percentage and time, long for 5 seconds to switch modes, charging mode: IN, discharging mode: OUT SET button: Short to view the currently set parameters; long the SET button to set the parameter DOWN button: Short to turn off/on the relay (emergency stop function), after the LCD display is OFF, the relay is disconnected type: Battery protector color:Blue Material:PCB+electronic components size:62 x 57 x 22mm Package Contents: 1 x Battery protector Only the above package content, other products are not included. Note: Light reflection and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.