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
A typical portable generator will put out about 6kw per gallon. That’s enough to drive a Tesla 3 about 20 - 25 miles under ideal conditions.
“If the portable generator burns.....”
Huge “IF”. That generator is highly likely a 120v circuit and that can take up to 40 hours to fully charge a near dead Tesla. That and having to charge the car outside, or at least run a very heavy duty extension cord from the outside generator to the garaged Tesla is just a major inconvenience. There are no scenarios where this is not a fail other than full on blackouts in California (which is a distinct possibility)
OK, I LOL’ed at your post.
That portable generator MAY be able to charge the car just a fraction faster than the parasitic loss of running the basic EV operating system.
I cannot say EXACTLY how many gallons the generator would require to reach a one-hundred miles charge. But I do know it will be a LOT more than one gallon!
Tesla in particular are notorious for their power drain even when “Off”.
One of the car test rags recently tried to recharge a test car on 110V in order to return it.
After three days they gave up and took it to a commercial charging station.
A small generator like that is less efficient than the 110V outlet.