Actually Tom, what I'm chasing is newer batteries, not a big torque-y drill (got enough of those). The C15 is exactly what I want because of the motor and trigger control. I ordered a C15 last month which had a 2011 build date on the drill but no markings on the battery. I checked with Festool and they told me there are no markings on the batteries and the best that I could do is assume the batteries were built around the same date the drill was built. I checked with my vendor who had some fresh stock shipped in from Festool and that drill was even older than what I had in hand. Knowing that the C15's in the UK started shipping with the 4.2ah batteries in Dec., I had hoped when we get them, I could be confident that the batteries included would be fresh. Why the fuss? Because I will not wear these batteries out from charge cycles, in my hands they will deteriorate with age. The newer the batteries, the longer they will go (for me).
The secondary consideration is interchangability of batteries if I purchase a cordless Carvex (that's a big IF). I haven't found the 3.0ah batteries on my LXT saws to be particularly good, so I'm assuming 4.2 would be better on the Carvex.
You are right about the weight of these batteries, and if the choice was 1.3 vs. 4.2 on the C15, I'd take the 1.3 hands down. But between the 3.0 and 4.2, the weight difference becomes a smaller consideration in the grander scheme. It appears the 3.0ah kits remain my only option, so it is what it is. I'll have to check with other venders.
Funny, I have the LXT platform as well, but the way I've used the tools, even the 3.0ah batteries were insufficient at times. [big grin] On one occasion I ran down 3 3.0ah batteries in about 15 mins (recip saw is great for trimming trees because it's so light, but there comes a point where you really should be using a chainsaw, and this was one of those times!). I recharged them after they cooled and finished the job the next day. These batteries are going on 8 years old, so I'm probably on the tail end of their useful life. When they are done I'll look into replacing them with 4.0 or 5.2 batteries if they are compatible with my tools. Despite people's complaints about their battery system, I've been pleasantly surprised.