IPhone 4 battery life rapidy draining while idle?

Last night I set an alarm on my iPhone. At this time it had around 80% battery so I was expecting it to have around 70% when I wake up. But when I did wake up (around 7.5 hours later) my iphone had no battery on it at all!
Please DON't ask me to send it to Apple because my warranty has ran out and I will have to pay £120 for a replacement, just tell me why its happening!

Use settings to your advantage. You can check what is draining the battery and make adjustments accordingly. Also, there are battery saver options. Some simple things you can do include lowering your brightness, and quitting the apps that are running.

Because when you first got your iphone you were charging it when it still had 20 or 30% left. You should of let it run down to the point where you have no battery whatsoever.

I did this with my iPhone 4 and the battery life lasts forever. I only charge it 4 times a week.

There can be many reasons for the battery drainage. Really depends on your use of the phone. Possibly battery is losing power to hold charge for long. If its jailbroken, it may consume more power, Your 3g might be left on. Really can't say much without having a look at the phone

Its hard to say exactly why it happened, but try closing the apps that are running in the background.

Have you been using a duplicate charger? Never use a duplicate charger, it will harm your iPhone. Use original chargers.

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