My Ryobi electric screwdriver/drill battery needs replaced. It's a cheap 9.6 volt unit. Home Depot doesn't stock replacements but they offered me 12.x and 18.y units. So I had to order from the manufacture ($32) and wait 2 weeks for delivery.
So, it looks like they purposely introduce a new voltage level every so often just to force you to purchase new equipment. Do all the equipment makers do this? Dewalt? Makita? etc.