If you think of the use cases they showed in the demo, they're not using the battery for extended amounts of time. The guy was playing while his dog did its business. That's a few minutes, maybe 15 minutes. Maybe half an hour if the dog wants to play a bit. My dogs usually tire themselves out at the dog park in about that time.

The guy playing at the airport, you might be waiting up to an hour. When he got on the plane, he plugged it in.

The guys at the basketball game seemed like they were killing time while they cooled down, maybe up to an hour.

The person at the rooftop party, she was at a party. They're probably not playing for hours.

The people in the car, I don't remember if they plugged it in or not but they could have, or they'd be playing on a short trip.

The one case where the person is in tablet-mode for an extended period of time, he sat down and immediately plugged it in. I wouldn't be surprised if we find an hour or two of battery life with the most taxing games.