Honestly, I've often wondered about the wisdom of offering so many batteries. It seems like Festool, like many other manufacturers, is leaning towards 18v. Everything even remotely new except the Ti15 uses the 18v batteries. What is the benefit of the T15 vs the T18? It looks like the 15 are only a few ounces lighter. It would make sense to me if they consolidated to 10.8v (or whatever the CXS is) and 18v.
(I know this ignores the C type drills, so I guess I could see a C12 or C15, but once you hit the 15, why not just go to C18) [big grin]