I hear ya,
It's a novelty, not a practical application.
And when you say I would need to power the "monitor AND laptop" - I'm saying I intend to build a cabinet that uses only a laptop as guts, no monitor, just that laptop's display.
As for the weight of "several car batteries" - I was thinking of a small footprint battery, like motorcycle. Not very heavy (for an adult to carry from the car to the location) and I estimate it would power a laptop for many hours.
I am thinking about building two. One that is very light and shallow for my daughter to bring with her when she goes away on weekends, and another that uses the battery.
It's about being entertaining and innovative really, it's just plain cool to have a truly portable arcade machine that doesn't require a plug.
Craig