Hi asian1
they used a 12 volt battery, for pratical pourposes.
A computer, needs at least even dual +/- 5 VDC or 3.3 or even less regulated voltages that they have obtained, from the only available source, the 12vDC battery (it is a mobile gear).
In a normal (not mobile) enviroment, it is better to have a PSU, with all the voltages needed.
For the LCD interface . . .why not
Ciao
