I'm a big fan of cordless tools, but you woluld need a HUGE battery to run a sidekick for more than 3 minutes. I find the weight of it perfect now, adding any more would make it awkward.
I think you're going to be really happy with it. The impact is just so handy... Nothing compares for sinking wood screws, teck screws and sheet metal screws; so much easier on the wrist.