well I am stuck on an island within an island and the building i work in is a no signal death trap. when ever i go in I make sure to take wifi, gps, and mobile signal off so that I only receive phone calls and text messages if I get lucky. I noticed that my battery lasted all day while I played games. It helps drastically to turn those off. If you turn airplane mode on then you wont get the call or the text when you have a bar or two. I had used my last 15% in 3 hours one time.
this was on my HTC Evo Shift.