Why does my iPhone battery die so fast?

I have boost magic, which is supposed to help my battery last longer, and I kill all my apps when I'm done using them. I go from 100 at 8am and I'm at 60 by 9:30am. And I hardly use it too, just to look up information quickly and I just set my phone aside. I let it go down to 20% battery and let it charge over night. It just started doing this recently. I also keep my brightness to pretty much 0 with the auto brightness on. And it still dies fast. What can I do?

Its a big phone it looses allot of battery Same with Android. Just turn it off When you don't need it or keep it on a charger When your not using it. Try to get a battery saver app it helps a little.

I have AT&T and I recently went to the store to ask why does it die so fast and they told me that we have about 150 times to charge our phone until the phone starts messing up. So all those time when we say "let me get a 5 minute charge" that counts as one charge. But the Apple store should switch your phone for you if this problem gets a lil outta hand. I'm about to do that.