IPhone 4 battery HELP!?

I have the iPhone 4 and it works great but the battery is pretty bad. I recently have a problem with the battery draining overnight and fixed it. I had it filly charged at exactly 700 am at 100% and now it's 5 21pm and it's at 26% and for the 6 hours I was at school it was in sleep mode. It says it has been used for 4 hours 47 minutes since last full charge and 10 hours 22 minutes in standby. I go through my multitasking bar a lot to erase all the apps in the background and have the settings set so they don't drain a lot of battery like: location services(off), notifications (off), auto brightness(on), mail fetch(off), and a few others to conserve the battery. Is it my phone or is there something I'm doing wrong? Please help!