Note, reducing the brightness of a DVD player makes huge difference in battery life.
Some manufacturers may sell extended batteries for more cordless life.
Is there a car nearby, see if the portable DVD has a cigarette plug in to get more life.
Just got back from a road trip. The rental van DVD system made a huge difference to keep bored kids occupied.
Some movies may have "digital copies". I wonder if that allows you to load the content onto flash drive so you can watch the movie without a spinning disk that would shorten the battery life.
