It's here, it's real--the genset trailer for your Makita powered car...

It's actually a trailer that houses more batteries to extend the range.
French startup releases a towable range extender for your EV
It's still ludicrous, but slightly less so than towing a gas powered generator.
From the story: "Little Generator Trailer Lets Electric Cars Go the Distance"
"If your battery starts running low, the EP Tender kicks into action, turning on the generator inside the trailer."