AnandTech reported the discovery earlier today:
While I'm somewhat skeptical sometimes of the accuracy of battery capacities as reported in FCC disclosures (which I noted about the battery size for the Nexus 5), these numbers seem credible given what I've heard, the statement Apple made during the keynote about the 5C battery size going up, and what I'd expect with some board re-layout for the 5S. The iPhone 5S ends up getting an almost 10 percent increase in size versus the iPhone 5, the iPhone 5C goes up around 5 percent versus the iPhone 5.
The iPhone 5 offered up to 8 hours of talk time on 3G, 8 hours of LTE Internet use, and 225 hours of standby time. Those times have been increased to up to 10 hours of 3G talk time, 10 hours of LTE Internet use, and 250 hours of standby time on the iPhone 5s and iPhone 5c.