Description:
The working PMU (Power Manage Unit)can be only worked for charging mode or step-up mode at the same time. (Without Battery)
If the USB-A interface without any external load (like Pi), with 5V input voltage of Micro USB, then the PMU enter charging mode.

The PMU will integrate a current-limiting resistor with the external voltage, 5V voltage for Lithium battery, around 4.6V-4.7V voltage for USB-A interface.

(The "ON" LED lights )
The PMU would enter step-up mode without external 5V voltage.

Under this circumstance, turn on the switch, USB-A interface can output maxmum 5V voltage, two USB-A interface can maxmum output 1.8A current.

The PMU itself has current-limiting protection. it will be short circuit when over 1.9A current

Packing Included:
1 X Lithium Battery Expansion Board