Note There is no limit how many batteries can be used only need to make sure the total capacity is 20000mAh Description This is the mobile power module Accessories 18650 Circuit board shell Meet the individual needs of your DIY but you must understand basic electronic assembly Features Motherboard comes with protection function Charging overcharge protection over discharge protection overcurrent protection Intelligent output device after charging full automatically stop charging to prevent mobile phones overcharge Output voltage and current stable will not harm user devices Specifications Micro USB input 5V 1AUSB Output 5V 2 1A 5V 1A Dual USB interface Charging display intelligent digital displayBatteries Type liquid lithium ion batteries 18650 3 7 lithium ion battery onlyProduct Size 57mm x 28mmScreen size 27mm x 17mm Installation instructions The circuit board is connected to the battery negative B B is the positive do not connecting reversed connecting reversed will burn the board the battery is connected in parallel welding assembling battery Note that the insulation between the battery and the circuit board battery lead not to touch the circuit board so as not to cause a short circuit Package included 1 x Mobile Power Bank 18650 Battery Charger PCB