During these warm summer months, I am getting up to 70 mpg with the Prius Plug in. I almost ran out of gas the other day, as after you go several weeks without getting gas, you tend to forget about it. That's 70 as measured at the pump, MUCH more when I do my usual 13 mile commute to my crane yard, usually several hundred mpg! That is with the 1200' descent from my place, with a fully charged battery, and keeping it under 60 mph. Best was 761 mpg, I can't do better as no matter what the ICE starts at some point, just to warm itself up in case it is needed. This is a bit frustrating when I see 9 miles or whatever left on the e only range meter, but makes sense if you're merging on a freeway I guess. The freeway ICE usage is what drags the mileage down, but never below 50 MPG.
I just bought a little Yamaha 1000 watt generator (lighter and quieter then the Honda, by just a bit) to run a AC unit for the cab of my crane (after a day spent in 104 degree temps, screw that) and have yet to secure it to my Travoy trailer and hook it up behind my BBSHD ebike.....but it has occurred to me. Before I do that, I will take all my batteries from my various rides, 46 AH worth, @ 52 volts, and get on the fat bike and ride, just because I can.
Here is where I want to do this: https://en.wikipedia.org/wiki/Gravelly_Range
An easy dirt road ride, but the high altitude would decrease my range and power.... oh wait a minute, that's right, electric motors aren't effected by density altitude, cool! I was thinking of the airplane, I've low flown this area many times, like less then 50' above the road, but still want to put rubber on the ground and ride it. I'll drive the Prius up there and charge my bike batteries while driving, then camp out that night with heat or AC in the Prius, it makes a great camper and mine is rigged to sleep in, fuel usage for overnight climate control is minuscule, thanks to the big traction battery and the ICE, when it does wake up to recharge it, running at optimum efficiency.
The only reason I have not done so yet is I get a great ride, "enough", on just my usual 11.5 AH battery, I guess I need to quite pedaling so much.