On Dagobah, as Luke is getting his MRE ready, he plugs R2 into a small glowy thing that presumably recharges the little tincan's internal battery.
Are we to assume that R2 units need to be plugged into something every once in a while to maintain usable lifestyle? If so, why not build that small glowy thing into the droid so that the human in charge doesn't have to carry around an extra piece of luggage?
And does this mean that all droids need to be plugged in at some point? If so, when does Threepio get to eat? And where is the plug on his body?