I think you would hit a minimum of 5 hours and if the lights are dimmed on the flight, you could probably run at the lower backlight setting which would get you more. If you run the movies from an SD or SDHC card, you may get even more battery life if the HD is sitting idle. I would also force the power saving mode to max battery life so the cpu is running at 800Mhz as it may work fine for movie playback and save some ore battery life – it is struggles (which I doubt) you can then run flick it back into normal mode!