I have an iPhone 4S. Previously when running on ios 5.1.1, my battery would drop at most 1-3% after a full cycle charged. i even set everything off or limit the iphone background usage. For exp: Only default notification is ON. Installed apps req notification is off, diagnostics & usage turn off, reduce the brightness & ON auto-bright, Location service is off, wifi off normally but ON only to surf, change to default wallpapers, force close all background running apps, clear or reset statistics every night, clear all recent call list, clear all messages. copy messages that are important to notes.
By doing this as from my experiences, my battery life drops 3%. unlock the lockscreen is faster, launching apps is faster. multitasking or surfing is also faster depending on our local 3G speed. i also clear safari cookies & data & also history to make surfing faster.
Everything i do is faster. i maintain my free space to 11GB. My usage is only 2GB++. When i feels like my photos are many or my video is taking up my space, i transfer all to itunes & i create another copy of my photos & videos just in case of accidents happens. So.. my 4S runs fast again.
Now.. as i upgrade to ios 6, my battery life drops to 2% & by doing the things above, it feels abit faster then before.🙂