Even if you close out all of your apps by double clicking the home button, there are still background processes running. The iPad doesn't have an Activity Monitor or Task Manager where you can see them like you can on a desktop OS or Android. A fresh iPad right after a restore will still have a usage counter that increases when Idle, just not very much. A better measure of actual usage would be "screen on time." I just do not believe that you're getting even close to 11 hours screen on time with 59% battery remaining. Is music with the screen off a huge portion of your usage? That would explain things.