Remove the bent battery terminal metal piece from the controller board battery pad. If removal of the bent piece is not possible, then flatten the bend. Drop a solder blob over the pad.

Put solder on end of battery terminal strip. Keep temperature between 250..270C degrees.

Lithium batteries degrade in heat. Put solder on battery terminal strip fast as possible.

Bend battery terminal strip with tweezers in slight "U" shape. It will put less stress on on strip while bouncing around.

Solder battery terminal to controller board pad.

Soldering the bent / torn battery terminal solved the flickering LED issue. The power bank now can charge a phone and itself.