A year ago I replaced the battery in my old iPhone 4 because the usage time had lowered to around 6.5 hours (that's usage time, not standby). The new battery brought the phone back up to 'new' spec and it gave me 8.5 hours of WiFi web browsing usage time again.
Anyway, I bought a brand new iPhone 5 three months ago and the usage time for WiFi web browsing was 8.5 hours. This was perfectly acceptable. I have now updated to iOS7 and my WiFi web browsing usage time is now 6 hours. That is worse than my old iPhone 4 with a two year old battery!
Two clean installs, setting up as a new phone and switching off parallax, location services, background app refresh, app store automatic updates etc have only permitted me to achieve 6 hours of WiFi web browsing before my battery is fully drained. Now call me a cynic but is this 'update' just designed to make all the old products obsolete so that everyone upgrades to an iPhone 5S?? My phone was the Apple flagship not one week ago!