Both batteries on my seven-year-old 12v Ryobi cordless drill/driver seem to be not holding a charge that is useful. It's my understanding that replacing batteries is nearly equal to the cost of buying a new unit so I'm looking for your recommendations on the best cordless drills. I'll probably want to go to at least 14.4v and maybe 18v. I sure see lots of Dewalt units in use. Are they the defacto standard?