Wouldn’t the better question be “so you burn a gallon of gas in the generator, how many miles will the Tesla travel on that charge?”
If the portable generator burns 1 gallon of gas, but I get 100+ miles range off that charge; that seems like a good deal to me. My Tacoma does 18-20 miles under perfect conditions
It will probably be cheaper to charge your testes that way rather than pay to upgrade your circuit panel for higher speed charging. It costs at least 4 grand to go from 100 amps just to 200 amps in an old house.
I just sent this picture to TWO Tesla owners.
Only a liberal would be stupid enough to think they could power their car down the highway with a 5 HP generator.