You make good points. Probably for the electric car owner (not you or I), renting another car with a regular engine makes more sense.
@thackney You are assuming,of course,that there will still be gasoline powered cars being manufactured to be sold to rental companies.
That is NOT going to happen. Within 20 years or so it will be illegal to own and operate a gasoline powered anything. Ford just announced they were be offering a battery powered Mustang next year,and I THINK it was GM that has already announced a date in the not so distant future when they will ONLY be manufacturing electric vehicles.
Nope,the simplest and best solution is my idea of a tow behind cart with a generator powered by the cart/trailer wheels when they are turning to spin the generator to charge the batteries in both the trailer/cart as needed. It's such a simple idea I can't understand why it wouldn't be obvious to everyone. The cart/trailer is going to be towed behind the driven car and the wheels will be turning anyhow,so why not have them spin a generator while they are turning?
If I were smart enough,I would patent this idea.