Can I use a Powerbank to supply power over USB when in the field?

[PeterDorr]

I am on a road trip and found that my 3 batteries are just not enough to take me through the day.
I have attached a Powerbank to the USB port and I am getting the impression that it helps a bit to lower the drain on the battery. Or is that just wishful thinking??

Thanks

[hugenoot]

I have only seen a loading icon when I connect the X1D to my MacBook Pro. But I didn't notice any change in battery life. During my trip to Vancouver Island I used a 12v to 230v inverter while driving...