You usually have access to power in long flights between continents and national train lines.

But you don't want to play that long on a portable device anyway, position is just terrible for your posture/neck and I don't think it is really healthy. What you want is alterning occupations: video games, reading, sleeping, drawing, card games, listening to music, making music, chatting, eating, moving in the main aisle, etc.

The planes used for long flights typically have power outlets, in my experience. Trains too but my experience is more limited there.