How to save battery life on i phone 4?

Turn the brightness down on your screen, if your out turn off wi-fi so it isn't trying to search for wi-fi all the time. If you have your email set up on your iPhone put the Fetch New Data to "Push" (that is so your account isn't reloading by its self every 15, 30 or 60 minuets, it'll only search for new mail when you open the app). Turn 3G and bluetooth off if you aren't using them :)

As mentioned in the previous answers, all of those are correct. But what most people don't know is there is something else you can also do to preserve your battery life even longer. ---> The iOS operating system differs from that of one that runs on an desktop/laptop computer. Every application that has ever been opened on your phone to date is still running in the background, causing your battery life to be sucked away at a pretty considerable pace. So, how do we fix this? First, double click the home button. This will either take you back to the home page, or pull up your recently used applications at the bottom of the screen. (If triple click home is on, you will have to tap this button three times) If the applications didn't appear at the bottom the first time, repeat this process once more. After you do this, press and hold anyone of these applications down for a few seconds until they start to wiggle about. You will notice, as soon as they start to do so, a red indicator pops up in the corner of each individual application. By clicking on this indicator, you manually shut each program down. This is the only way to shut programs down, and it is recommended you do so before each charging session. Your phone will operate cooler, glitch less, and your battery will last much longer.

the ways to save battery life is: -turn of wi-fi when not in use -turn off bluetooth -turn off gps -turn off data sync -turn off automatic updates -turn the brightness down to a level you can manage with. -try not to play too much games on it

Read this BLOG: http://www.technewscorner.com/2012/02/iphone-4-battery-drain.html I followed the advice and am noticing a good difference in my iphone 4 battery life....

Turn Brightness Down Low. When Playing Music Turn It Off By Clicking The Button On Top :) And I bet that's all u use anyways :P

Buy a rechargable case i have one and it works awesome