By setting the upper limit voltage UP and the lower limit voltage ; when the battery voltage is less than or equal to the lower limit voltage , the relay turns on and the charger starts charging the battery; when the battery voltage is more than or equal to the upper limit voltage UP, the relay disconnects to complete an automatic charging; when the relay turns on, IN flickers, indicating that it is charging. Discharge mode OUT By setting the upper limit voltage UP and the lower limit voltage ; when the battery voltage is or equal to the upper limit voltage UP, the relay turns on and starts discharging; when the battery voltage is less than or equal to the lower limit voltage , the relay turns off and completes an automatic discharging function; when the relay turns on, the OUT flickers, indicating that it is discharging. Note: This product is a simple voltage controller. It can turn on and off the output by relay. It only plays the role of switching, and can not change the voltage. Calculation of Voltage Percentage: Battery Voltage/(Upper Voltage-Lower Voltage) Key function:Short press UP button, switch display% and time, long press 5 seconds switch mode, charging mode: IN, discharge mode: OUT SET key: Short Click to view the parameters currently set; Long press SET button to enter the parameter setting interface, set UP: voltage upper limit, : voltage lower limit, OP: turn-, : delay turn- (0-999 seconds), FOP: forced turn- (0-10 seconds) in discharge mode. Short press DOWN button, turn off/turn on relay enable (emergency stop function) turn off, LCD display OFF, relay disconnect Long press DOWN button to set the status of LCD backlight L-P: OFF backlight constant brightness, ON: backlight automatically extinguishes after 5-10 minutes; after extinguishing, any key wakes up. Parameter Settings: Enter the parameter setting interface by pressing the SET key for a long time; After entering the parameter setting interface, switch the setting parameters by pressing the SET key. After choosing parameters, it can be set by UP/DOWN key to support short press and long press. To set other parameters, repeat steps B and c; After all parameters are set, press SET key for a long time, exit and save; Colour:blue black Material:Plastic, metal Package Contents: 1 * Solar Battery Charger Controller Only the above package content, other products are not included. Note: Light 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.