Can’t answer #1, but I have a thought for #2
I wanted to build a project which would requires 12v. I found a MicoUPS [1] which takes 12v in (easy to get, any standard wall wart for example.) and puts 12v back out. The important part is that it powers off of Lead Acid (SLA) batteries [2], which are super cheap (of course). The last component was a DC/DC converter which could take the 12v output and tune it down to 5V for Arduino’s [3].
Not saying it’s a complete solution, but an 18amp hour SLA will probably run a small arduino for a significant amount of time. Of course, if you needed more, there is also the option of connecting the batteries in parallel (not sure how that would be handled by the PicoUPS).
-Jon
[1] mini-box.com/picoUPS-100-12V … tegory=980
[2] amazon.com/UB12180-Sealed-Le … -20&sr=8-1
[3] sparkfun.com/products/9370