It seems to me that an overnight charging might be eliminated or reduced if you let the momentum of the car turn a generator (charging unit) that would continually charge the unit while in motion much the same as an alternator. A fifth wheel under the car making contact with the road would turn the generator and charging the batteries would increase mileage especially at night when lights would create an even greater drain on the batteries causing them to drain much quicker than during the day. A charging unit could even be installed to one of the exsisting four wheels rather than a fifth wheel. Either way it seems to me that lead acid batteries fair better with a constant charging rather than when they are almost exhausted.