One could make a mini-itx computer, connect a battery to it like a UPS perhaps the size of a laptop battery.. But then for screen and keyboard, how hard would it be to connect a laptop to the mini-itx ...
I couldn't really decide which forum to put this in. It's part A/V, part mobile and part other hardware. What I want is a cheap way to carry a monitor/mouse/keyboard with me for when I have to ...