This tiny board is all you need to build your own power bank using 3.7V Lithium batteries. It charges as well as steps the battery up to 5V for your projects.

Built-in charge and discharge
Charge status indication. Red light flashes when charging; Long red light when full. While boosting to 5V the blue LED will be flashing indicating that the 5V for your projects is available.
The step-up charging board can be connected to a lithium battery and connected in multiple sections of lithium batteries, as long as the voltage is 3.7-4.2V in parallel (only be connected in parallel, not in series).
It has protection functions, protecting from over-charge / over-discharge/ over-load.

Power bank circuit board product introduction:

1. Input Voltage: 3.7V~5.5V
2. Charging Current: 1A (max)
3. Output Current: 1A (max)
4. Output voltage: 5V
5. BAT Discharging Stop Voltage: 2.9V
6. Discharging Efficiency: 85% (input 3.7V output 5V/1A)