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.

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 1A
USB Output: 5V 2.1A / 5V 1A(Dual USB interface)
Charging display: intelligent digital display
Batteries Type: liquid lithium-ion batteries (18650)
Product Size: 57mm x 28mm
Screen 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.