The world needs a new source of energy, an unspillable source.

ABOUT HYBRID ELECTRIC CARS?

Why, instead of using 2 engines, they don’t get rid of the combustion engine and replace it with a gasoline generator engine to charge the batteries as soon as they get to certain low level, once fully charged it will disengage till the the batteries get low again…and so on. This engine would be much smaller.
My reasoning is that, it’s easier to spin a generator with a small gasoline engine to produce electricity, than propel the whole weight of a car. Also by getting rid of the combustion engine the car would be lighter; We could also aid the Generator with electricity regenerative devices placed on spinning parts of the car.
why can’t this be done?, Is it not economically viable? What would be the problem with this configuration?
Can someone explain this to me?….thanks!