I took a screenshot whenever my iPhone gives the 20% battery warning, then plugged it in. On iOS 6, my 4S got 6:37 of usage time (mean of 17 points) On iOS 6, my 5 got 8:57 of usage time (mean of 15 points) On iOS 7, my 5 got 6:47 of usage time (mean of 7 points) So...2 hours sacrificed for iOS 7. Worth it, in my opinion, but a big price to pay for sure. The mean and median were very close in all cases. I had background app refresh and location history off in iOS 7. I hope iOS 8 doesn't have a similar effect.