I have found the Ryobi 18v line to be very interchangeable... to the extreme that even the newer longer lasting Li ion batteries work with their older originally NiCAD based tools. (I think they call the system "Plus1")

Of course they did "step up" from 12 volts some time back, and thus rendered my old 12 drill motor to the "scrap heap." (I plan on turning it into a 12v plug in tool and put a cigar lighter plug on a cord onto that drill.)

I think the big line you are speaking of is Dewalt... with the radio/charger things. While I might decry the loss of cords, I have found most of the battery operated tools operate fairly well... but I doubt a worm drive saw, working all day long, would have a ghost of a chance if it were battery operated.