I have two cell phone batteries soldered on the back of my n800. I get 12 hours of runtime. With 12 batteries my n800 could have relieved the boredom on that trip.
I very much doubt you'd get anywhere near that figure in real world situations. This was a car sitting at a single speed (40 km/h for that matter) on a closed track. I imagine it's a lot like the Tesla... use it hard and it'll die in 30 minutes.