Four Ways to Make Your Battery Last Longer - NYTimes.com
Instead, Nicole pointed out a few things that were contributing to my friend’s rapid battery depletion. I took notes and thought I’d pass them along.
* Push e-mail. This, I believe, was the big one. My friend has seven e-mail accounts, and her phone was checking each of them every 15 minutes. If you turn off the “Push” feature, and set it to Manually instead (in Settings->Mail, Contacts, Calendars->Fetch New Data), then your iPhone checks for e-mail only when you actually open the e-mail app. Your battery goes a lot farther.
(If you have a corporate Exchange account, your calendar and address-book data will similarly be updated only when you open those apps.)
* GPS checks. In Settings ->General->Location Services, you’ll see a list of all the apps on your phone that are using your phone’s location feature to know where you are. (It’s a combination of GPS, cell-tower triangulation and, on some phones, Wi-Fi hotspot triangulation.) All of that checking uses battery power, too. My friend had dozens of apps with Location Services turned on, many of which didn’t really need to be on. She turned most of them off.
* Notifications. Similarly, in Settings -> Notifications, you see a list of apps that are allowed to display pop-up notifications (those blue text bubbles that look like text messages). To do that, they have to monitor what’s going on with your phone — and that takes juice. Turn off the ones you don’t really need.
* Background apps. Nicole the Genius discovered that my friend had a huge number of apps open — maybe 40 of them. She maintained that they were using battery power, too, in the background.