Interesting, T+ for the initiative!
So if we are looking at the specs, should it be able to power a rig for one festival day (assuming overnight charging inbetween), or a multi-day festival without charging?
In my case, I'd be satisfied with one day runtime (6-7 hrs), and less weight to carry.
Also, are you planning for more than one simultaneous outlet with different voltage (like the 5V/9V box for JB3+UA-5)? Or just one outlet at a time?