The circuit board is simply connected to the battery negative B-, B +. Please note that you can not reverse the polarity. Connecting reversed polarity will burn the board. also, 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. This board comes with several protection functions such as, charging amp; overcharge protection, over-discharge protection, overcurrent protection. This is an intelligent output device that automatically stop charging after device is fully charged. Micro USB input: 5V 1A Dual USB Output: 5V 2A / 5V 1A Charging display: Intelligent digital display Batteries Type: Lithium-ion batteries (18650) 3.7 lithium-ion battery only Product Size: 57mm x 28mm Screen size: 27mm x 17mm Type: Electronic Accessories Brand: Other.