If it fits, it will probably work, but the drill will run more slowly. However, DON'T CHARGE THE 14.4v BATTERY WITH THE 18v CHARGER!!! YOU WILL DESTROY THE BATTERY AND MIGHT WIND UP SCRAPING ITS REMAINS OFF THE WALLS!!!!!
Probably not, as DeWalt is smart enough to realise if they have 2 different voltage batteries that someone MAY try to interchange, they should be different in some way so it cannot happen, e.g. like in putting a 14V. battery on an 18V. charger, or wanting to do what you are suggesting, which would be useless, and cause harm to their reputation.
Yes, make no harm to drill but drill torque lost almost half.
