Day 1 with iOS 7
Along with about a gazillion other iPhone users, I downloaded Apple's iOS 7 update yesterday. So far, it seems like a vast improvement over a previous version I didn't even think was broken. (One unanticipated advantage of stripping all those 3D elements and skeuomorphism in favor of a new "flat" design? What feels like a huge boost in speed and smoothness.)
But I found this TUAW blog post by Mike Wehner about managing battery life in iOS 7 interesting. Several of the new features (allowing apps to refresh their data in the background, for instance) can cause a drain on battery life — and I'd already become concerned about how often I'd been having to charge my old iPhone 4S even before upgrading.
Some of the suggestions weren't necessarily new — making careful decisions about which apps can keep track of your location, for instance. To limit an app from using your iPhone's built-in GPS, tap Settings → Privacy → Location Services. You'll find switches you can use to allow or forbid each of your apps from finding your location, as well as a master switch to disable all of them at once. Little pointer symbols mark the apps that have recently used your location, have used it within the last 24 hours, or are using your location for "geofencing" — generating alerts when you arrive at or leave locations you've defined.
Others are new, like that background data refreshing I mentioned. Look for those settings by tapping Settings → General → Background App Refresh. You'll find the a list of apps and switches similar to what I described for your location services. This time the little pointer symbols indicate apps that use your location in the background, including those geofences.
You can also cut back on iOS 7's fancy 3D motion effects, like those wallpapers that change perspective as you tilt your phone. Just make sure you show it off to your friends first, if your the type who loves to do that. Tap Settings → General → Accessibility → Reduce Motion and turn on the switch you'll find there to keep your phone from burning battery to do all that math.
(While we're at it, think twice about choosing one of those new "dynamic" wallpapers with the moving backgrounds. Your phone's processor has to handle all that motion, and running the processor sips power from your battery.)
My iPhone 4S doesn't support the new AirDrop feature, but Wehner recommends turning it off when you don't need it. It takes power to find other AirDrop users around you, so it just makes sense to switch it off when you don't need it. Fortunately, the setting is easy to change in the Control Center — just swipe up from the bottom of your iPhone's screen and tap the AirDrop button.
Other sources of battery drain might just take some time and familiarity to find. I noticed my phone downloading cover art for all the albums in my library after I upgraded, for example, to support the new Cover Flow display. (That's what you see when you turn your phone sideways while looking at a song that's playing in the Music app.) All that downloading must burn some battery, too, I figure.
But I haven't found anything in iOS 7 yet that makes me regret updating — and I've barely scratched the surface of, say, iTunes Radio, Apple's new Pandora-style music streaming service.