The 300 mile range is likely under ideal conditions. Using the air conditioning, heater, defroster, lights, radio or windshield wipers will reduce that range. Also environmental factors affect battery life...below freezing temperatures or temperatures above 100 degrees. Consider the hours long charging time if you are on the road..longer still if you have to wait at a charging facility while someone else is spending hours recharging.
.
Consider the coal that has to be burned inefficiently to power them!
.