Descriptions:1. Output voltage: 2-4 series lithium battery or lithium iron phosphate battery (can be adjusted by external resistance).Suitable for 2-4 series lithium battery or lithium iron phosphate batteryLithium battery 4.2*2 string = 8.4VLithium battery 4.2V*3 string = 12.6V / 4.2V*4 string = 16.8VIron lithium battery 3.6V*3 string = 10.8V / 3.6V*4 string = 14.4V2. Solar cell maximum power point tracking (MPPT) is to ensure that the light intensity changes, the photovoltaic cells have been the maximum output power to take full advantage of solar energy. In general, it is necessary to use the switch mode DC-DC converter to achieve MPPT function, to maintain the output voltage and charge current product (output power) to maximize.3. CN3722 is the use of switching buck mode DC-DC conversion way to achieve the maximum power point tracking function of photovoltaic cells, the input voltage up to 25V, very suitable for input voltage and battery voltage difference between the relatively large applications.Features: High-end technology MPPT solar maximum power tracking charge management chip, with trickle, constant current, constant voltage charging management.    The use of imported high-frequency low-conduction resistance double MOS tube, high current diode, high efficiency flat high-power inductors, alloy current detection resistor.    The large aluminum cooling fin at the bottom, ensure it keep stability working at the high current.    High-speed and efficient way of charging, heat small, fast.    Dual status indicator light, no battery when the red light flashes green light is always on, charging red light, full of self-stop while the green light.Specifications:Input voltage: 18V nominal solar panels (no load about 21V solar panels)Output voltage:Output voltage: 2-4 series lithium battery or lithium iron phosphate battery (can be adjusted by external resistance)Output current: maximum constant current 3A (Charge current > 2A, please add heat dissipation)Wiring method: Welding plateIN + : input positive,      IN - : input negative (SOLAR)BAT+: battery positive,   BA-:  battery negativeSize:45* 31mm/1.92*1.22inchPackage Included:1 x MPPT Solar Panel Controller