the "old" nexus one can stay charged for over a week. of course I have a 2400mah battery and switched to edge, but after the tornados here, lots of things are necessary.Google will push updates much faster, however, all of them are BETAs
Also I'm wonder answer to this question:
How long can ur Nexus S hold with each charge?
switching to a powder saving profile, with a double size battery will yield very good usage, for a smart phone.
I'm sure this is possible on any platform.