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Aside from taking the steps to decrease power consumption that were mentioned in the first response to your question, the least intrusive way of adding battery life that I've found is a Mophie Juice Pack Plus case. As the name suggest, it's a case, but it also includes a 2000 mAh battery. I don't think that these are out yet for the iPhone 5, so you might want to hold off a little white before you pick one up since you are looking at getting a 5 soon. You do give up some of the sleekness of the "naked" iPhone, and with the case on it will be noticeably thicker and slightly taller, but at least you won't be all lumpy.