I've had the Dewalt 20v impact driver, drill, and a circular saw + a vac for a while now, for me, the battery life is not a problem, generally I charge a battery when I think of it rather than when it's been run flat.
As for power, not an issue either, the drill or the impact driver can drive a screw completely through a 2x4 if you want to. I've used the saw to cut notches in 4x4 lumber with the entire cutting capacity buried in the wood with no issue at all. I've also cut 5/4 Maple with it.
If you haven't used a modern cordless drill (or any other modern cordless tool, for that matter), you may never pick up a corded one again.
Also, Dewalt is doing some interesting stuff with battery compatibility, the batteries for the 40 and 60 volt tools can also power the 20v tools.