At a constant speed the “friction” forces that the motor has to over come are rolling resistance, friction in the power train to the wheels and drag. Of those three, only rolling resistance is a really a big function of the car’s weight. At highway speeds the drag on the car is significantly more than rolling resistance (several times more). Unless you do a lot of stop and go / accelerating or drive at low speeds (< ~25mph) the range of the car is effectively independent of the weight of the car at long distances.