Why My iphone 4 battery is draining so fast, even if it's lock or not in use?

I'm very curious about my iphone since last week. For example. I fully charged it before i sleep then the next morning i'm so shocked that the battery is only 57%. What the f*ck is that!

Double click your home button, press and hold one of the apps on the bottom of the screen until the shake and a red x pops up, then close all your open apps. Make sure your Wi-Fi is off and turn off your auto dim for your screen.

You shouldn't have installed iOS 7.It's a battery hog.
Check the cnet website for a howto on turning off some of the unnecessary "features"

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