It’s not a 40kw generator, it’s 130kw!
“Stellantis estimates the range of the Ramcharger to be up to 690 miles, including up to 145 miles powered by a 92 kilowatt-hour battery when fully charged without the extended-range power from the gas engine and 130 kilowatt electric generator.”
All kidding aside, about a year ago I read about a cross country off-road rig that did this with a fairly small set of batteries and a reliable good generator, probably a Honda, that just ran at a steady rpm like most generators do.
If I remember correctly this shop-built side by side rig could go over 2000 miles on one tank full of regular gas. It was made for off-road use so I assume the speed was kept under 40 mph most the time with occasional bursts of 50+ mph.
I believe this was a one-off built as proof of concept.
Here’s a company that manufactures hybrid side by side’s. https://www.huntve.com/copy-of-onrange-4x2-1