Android users get a handy app that tells them which processes are draining their phone's battery, but iPhone users have to guess. The good news is these aren't generally big mysteries. Here's how to arrest the biggest battery-draining culprits.
1. The screen is one of the biggest battery drains, so decrease Auto-Lock time if possible to keep it off when it's not needed. One minute is the minimum allowed. Also, dim the overall screen brightness to the minimally comfortable level by visiting Settings > Brightness & Wallpaper. Turn Auto-Brightness off to manually adjust it.
2. Shut off radios you don't need. If you primarily use your phone while connected to Wi-Fi, you can shut off the more power-hungry cellular data to save power. Visit Settings > General > Cellular to find these options. Shut off all radios on this screen (the options will vary based on which iOS device you have).
3. Shut off Location Services (Settings > Privacy) as well, and turn off Bluetooth (at the top of the Settings menu) if these are not actively being used.
4. Turn off Push email and decrease Fetch time. Apple actually warns you that Push email (which essentially checks for new messages constantly) will drain your battery quickly. Turn this off under Settings > Mail, Contacts, Calendars > Fetch and select Manual.
5. Turn off Notifications. This reduces CPU load a bit. Under Settings > Notifications, scroll down to the Notification Center and configure each app individually.
6. Not using iCloud? Shut these services off as well under Settings > iCloud.
7. Lastly, you can get a better handle on your overall battery life if you turn on the battery percentage meter (instead of having just the difficult-to-discern icon) by visiting General > Usage and turning Battery Percentage on.
More: 11 Battery Tips for Your iPhone 5