If your iPhone battery seems to be holding less and less of a charge here are some ideas to help make it last longer.

Push e-mails: If you have a number of emails accounts, your phone could be checking them as often as every fifteen minutes. If you turn off the "Push" feature, and set it to Manually instead, then your iPhone checks for e-mails only when you actually open the e-mail app. Your battery will go a lot farther.

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. That checking uses battery power. Turn as many as you can off.
Notifications. Similarly, in Settings->Notifications, you see a list of apps that are allowed to display pop-up notifications. They monitor what's going on with your phone-and that take power. Turn off the ones you don't really need.

Background apps: Make sure you do not have a huge number of apps open. Again, battery power is being used in the background. Quit all of the apps that you can. Double-press the Home button to open the multitasking app switcher. Hold your finger down on any icon until they all start wiggling. Tap the little X close boxes to manually quit open apps.

Now watch your battery and hopefully you will have power longer.

source: New York Times: David Pogue