DC 5V 2.1A Charge/Discharge/Boost/Battery Protection/Indication Module 3.7V 4.2V Lithium Batter 4 in 1 Charge/Discharger/Lithium Battery Protection/Battery Indicator Module Specification:   Charging current: 0-2.1A Charge quiescent current: 100uA Discharge current: 0-3.5A Discharge quiescent current: 50uA Discharge conversion efficiency: Max 96% Output current: 0-2.1A Operating temperature: -20~85℃ Size: 26.7*18.1*5.7mm Weight: 1.9g    Comes with battery protection functions, do not need battery protection board: Overcurrent protection(OCP) Overvoltage protection(OVP) Short circuit protection(SCP) Over temperature protection(OTP)    Pin description: VIN: Charging port + GND: Charging port - BAT: Battery port + GND: Battery port - GND: Output port - VOUT: Output port + KEY: Output trigger port(Low pulse trigger)   How e:   1. In discharge mode(In the charging mode, the KEY function is invalid), trigger the KEY once - turn on the output; Continuously trigger KEY twice - turn off the output. 2. When connecting the load for the first time, it will automatically turn on the output. If the load is less than 50mA, the output will be turned off after 30 seconds; If the load is more than 50mA, it will continuously turn on the output.