For the past 1.5 years, I've been using a Panasonic DVD-LS55 7" portable DVD player, which now seems to have been replaced by the DVD-LX95, a 9" player. I purchased the LS55 because of the battery life -- it lasts at least 8.5 hours after it's been fully charged (I don't know its absolute maximum as I've never used it for more than 8.5 hours without recharging). It's sufficiently small that carrying it onboard isn't too onerous (though the TSA security folks often don't seem to know what to make of it and ask, accusingly, whether someone forgot to take their laptop out of its case), and it fits nicely in the seat pocket in front of you should you want to stow it for a while. It seems pretty sturdy, and I've been very happy with the video and audio quality. The screen on the Panasonic is really flexible and the unit as a whole doesn't take much space, which is handy given the small amount of space on the tray table, especially if the passenger in front of you decides to recline. I completely agree with your cost benefit assessment -- the money you'll have to spend if you're looking for a long battery life is hard to justify unless you're going to make substantial use of the unit. However, my brother, who has the same DVD player, tells me that it was hugely popular with my usually very fidgety niece (brother and sister-in-law, too), and made their flight from Munich to Chicago pass quite uneventfully.