I have learned that it uses up all of your reserves to keep looking and looking for something that you should know is not out there to find. To conserve your power, you need to stop struggling and stop seeking, in those situations.
I am talking, of course, about the settings on the iPhone. If you are in an area without wireless, the wireless setting should be off. If you are in some remote part of Vermont with no cell phone coverage, your phone should be set to the no-call “airplane mode”, or just off. Otherwise, you’ll run down the battery in record time.
I learned other ways to conserve battery life from this: http://www.apple.com/batteries/iphone.html
Jane's Lessons Learned 