Wouldn't it be more efficient for long trips to run a small generator in the car that charged the batteries?
A car engine needs to deal with variable power/torque/etc. It's got transmissions and radiators and all sorts of extra complexities. A generator runs at one speed and is efficiently tuned to that one speed. If you suddenly need more power to accelerate then that would be provided by the batteries. Batteries are like >90% efficient. So going motor->battery->wheels seems like you wouldn't loose much even in the worse case of coasting on the highway at an ICE's optimal speed.
Generators are also generally simpler and smaller. You could envision one that you could pop into the frunk when you need extra range. It would continuously recharge your batteries as you drive - even before they're depleted. Even if it didn't recharge as fast as you were using up power - you'd still drastically increase your range. Forthermore you could leave it running overnight to charge your car if you're in some remote place with no charging stations
Literally nobody has done this - so there must be some reason I'm overlooking :)