Would you mind carrying a portable battery about the same size as the phone that can recharge the phone via USB? (this is my solution)
Something like this: http://amzn.com/B005X1Y7I2 seems to be small enough to be pocketable while having enough juice to help you out if you need it.
The only problem I would have is remembering to keep the thing charged.
And with USB being so standard and available pretty much everywhere, it almost seems like a non-issue. It's not like back in the day when you had to have separate car chargers for different phones for example. I've seem USB charging ports in trains, airplanes, airports, hotel rooms, portable camping battery packs and even some power extension cables.