*Probably to test how code performs under such low power conditions?*
not really. he's developing for mcu's. not for the system itself, so that has no point.
for it to be portable, it would need to have some other stuff.. like a monitor, keyboard and other stuff all which take power. now he might be doing it under solar power at his cottage or yacht or whatever.. but then kind of still would be needing the monitor and other peripheals.
basically the answer is just buy a friggin netbook. even if you need to have usb programmers for the stuff you're going to program due to not having gpio right on the system. my bro uses a raspi for mcu development but that's just mainly for flashing from the thing and using ssh to connect to it from a computer. so if he just wants to attach a big battery to the thing and leave it at where the mcu is doing some controlling or data acquisition and wants to update it live there.. then get a raspberry pi.