The Monolithic Power Systems (MPS) MP2636 is highly-integrated, flexible switch-mode battery charger with system power path management, designed for single-cell Liion or Li-Polymer batteries used in a wide range of portable applications. It is really simple to use, once you plug a lipo battery, it will work like a power bank. When there is an external power supply from VIN, it will charge the battery automatically, and the CHG led will light up; when there is no external power, only battery on battery port, the Boost will be ON.