The Pi is now powered by 2a wall wart, but I have 12 Vdc adapter to go in a car or battery pack and I also have solar panel to charge up my battery pack that I made up years ago for all my radios to operate off the grid.
Here is the Pi / Dv4mini fully operational with wifi to hotspot on my iPhone
And all of it controlled by my iPad on the same hotspot from my cellphone.
