BMW did it long ago in the i3 with the range extender. Not the best attempt though. They made it tiny, but it still had a heavy battery (though obviously not a very big one, just heavy for a car of this size), so to get the weight down, they used carbon fiber, but it was supposed to be an economy car and now with carbon fiber it was expensive.

Idea itself is not bad though.

this is a great idea! love it. can we skip the small engine and just install a small fission reactor instead?

Was the gas engine like a trickle charge?

I've been asking forever why we aren't seeing gasoline electric vehicles. It's literally been standard practice for diesel locomotives for basically as long as diesels have been dominant, you hook a gigantic diesel generator (prime mover)to a pair of gigantic electric motors (traction motors), and when you want to slow the consist without consuming your precious air for more intense braking, you can just turn the motors into generators and dump the energy into giant resistor banks on the roof (dynamic braking) or into an battery powered engine behind your diesel electric engine

You get the power of electric motors, the mechanical simplicity of electric transmission, and the range and rapid refueling of an internal combustion engine. The disconnect between the prime mover and the traction motors means each can be tuned to their respective efficiency curves (especially if a bank of batteries/capacitors is included as a buffer) so you get more efficient idling, more efficient acceleration adds the options of connecting slugs (units with no prime mover nor control cab) or b-units (units with no cab)