Power Arduino Nano with OTG cable
It is possible to use a OTG Y cable just plug it into your phone, power cable into the power source and use the third connector to connect  to your PC. (Assuming the PC only gets GND, D+ and D- and battery bank GND, 5V) 

It is also possible to reprogram an Arduino with an Android device that has OTG support.
Would save you a bit of hassle. 

My Android phone (LG D605) with ArduinoDroid can easily upload code to my Nano and Uno.