Vita and 3DS both have HORRIBLE battery life. with all the shit turned off and darkest backlight setting you're only gonna get 8 hours tops and realistically it'll be less then that. Pretty impractical for bus or plane rides. My iPad getting mad hours of battery life with wifi and netflix running. Vita with 32GB memory card is over 400 dollars. Add a game or two and you're looking at 500. That's pretty expensive for a portable gaming unit.
no worries, planes these days have USB at each seat to plug into a power source.