It would make absolutely no sense whatsoever for them to release an updated and upgraded iPhone that has a worse battery than the previous one.
Didn't the iPhone 3G have a worse battery life than the original iPhone? If yes then I worry that we might see history repeating itself.
History - launch a significant new feature (3G capability) but at the expense of battery life (the iPhone 3G) and then address the battery life issue the following year (the iPhone 3GS).
History possibly repeating itself - launch a significant new feature (bigger screen) but at the expense of battery life (the 2011 iPhone) and then address the battery life issue the following year (the 2012 iPhone).
I can't think that the A5 will save much if any power under low CPU load conditions which, unless you're gaming or watching video, is most of the time for most users and I worry that a bigger screen, especially if it's the rumoured 4" one, will add a fair bit to the power draw.
What could Apple do about it? Well, it's just possible that part of the reson for the delayed iPhone launch this year is to get an A5' chip ready that is basically an A5 on a smaller geometry (32nm?) and, if they haven't managed to get that into the 2011 release, then I think most informed commentators would be really surprised if Apple's 2012 lineup of SoCs weren't on a sub-45nm geometry; that's virtually a given in my opinion. Also, I'm no expert on display technologies, but maybe at the same time as going up to a bigger screen Apple might also manage to introduce some sort of power reduction technology to at least stand still if not actually reduce consumption in going from the old screen to the new bigger screen and again, if they haven't been able to do that in the 2011 timescale, maybe it might happen for the 2012 model.
No one knows, but on the assumption that the rumour of a bigger screen is true then I would be relieved and somewhat impressed if Apple manages to maintain the battery life, not at all surprised if battery life takes a hit, and very impressed if they manage to get any worthwhile increase in battery life (better than 5% gain) with a new model that features a 3.7" or larger screen.
- Julian