Project 13 - fails when powering Arduino via power bank

The project works as expected when Arduino is connected via usb to the laptop.

I comment out the Serial communications and try to use the project with Arduino connected to 5v power bank and it fails to light up the LED.

Why? I suspect a grounding issue because the laptop is grounded w/3 wire plug but the power bank does not.

How do I resolve this so it works when running via alternate power sources for portability?

How did you connect the power bank with arduino? to 5V port and GND?