Why is my iPhone 4 battery draining extremely fast?

I know iPhones are notorious for having low battery life and needing to be charged pretty much everyday, however, today I noticed something strange. I charged my phone this morning and unplugged it when the battery reached about 30%. Since I barely use my phone during school I figured this would be enough. I went to school and accidentally left my phone in my locker for the first four periods (so that's about 2 hours and 45 minutes). Since it was in my locker, it was impossible for me to have used it at all. For some reason when I came back to my locker to get it, though, it had completely run out of batteries and died and said I needed to plug it into a charger? It was also warm. At first I thought the only logical explanation was that someone had been using it for that whole time but it was locked in my locker and no one knows my combination or would even have the time to use my phone for the first 4 periods of school. Anyone have or had this problem? Anyway I can fix it without a visit to the apple store? Anything will be greatly appreciated!

It probably because the apps you are running in the background to Official close them press the button
on the botton center of the device twice really quickly then keep holding one of the apps until they shake then close them hope this help peace #D

All phones need to be charged everyday. You can't sit there and text all day and then wonder why the battery is at 20%.

Clear the multitasking bar. When on the home screen, double click the home button and Hold your finger on one of the apps until they shake and a little ex is at the top of each app. Clear all the apps. It should help conserve your battery.

Stop Running Programs:
1) Double Click the Home Button
2) Long Press on each application until it's shaking then click on the red X to close out of it

Turn off Wi-Fi
1) Go to Settings
2) Click on Wi-Fi
3) Click on Off

Turn off BlueTooth:
1) Go to settings
2) Go to General
3) Turn Bluetooth Slider to Off

Reduce Screen Brightness
1) Go to Settings
2) Go to Brightness
3) Put the slider to about 1/4 mark or lower (your eyes will adjust to the dimness)

Turn off Auto Brightness
1) Go to Settings
2) Go to Brightness
3) Turn off Auto Brightness

Turn off Wi-Fi
1) Go to Settings
2) Go to Wi-Fi
3) Turn off Wi-Fi

Turn off Location
1) Go to Settings
2) Go to General
3) Go to Location Services
4) Click on the top option to disable all location services
* Select Certain apps that you don't always use to disable location services for them*

Turn off Push Email
1) Go to Settings
2) Go to Mail, Contacts, Calendar
3) Select Fetch New Data and Slide to Off

Fetch Less Often
1) Go to Settings
2) Go to Mail, Contacts, Calendar
3) Select Fetch New Data
4) Choose Either an Hour or Manually (When you wake up your phone after it being asleep you'll also be notified of all of your new emails via a red circle with a number in it on your mail icon)

Auto Lock Sooner:
1) Go to Settings
2) Go to General
3) Go to Auto Lock
4) Select 1 Minute