For example, if a 1/18 car and a 1/8 car uses the same battery, say a 11,1 volt LiPo on 3000 mAh's, you can charge the batteries using equal chargingtime on both with a charger. But the 1/8 car, due to being bigger and heavier, will drain the battery faster than the smaller 1/18 car. It depends also on what charger you have, but if you get a computer charger you can adjust everything you want and charge a battery safely in one hour.

Your question was a little strange in my opinion, i hope i read and understood it right. So; the same chargingtime but different runningtime!