You see there are some very common reasons to experience battery drain as follows:
After checking on all of the above items and if you have everything turned off and you are still getting super fast battery drain, it’s most likely a bug. Sometimes there can be an app that has caused some sort of exception and caused a zombie process to spawn creating some form of resource leak which is draining your battery. In these situations there is only one thing you can do. You have to re-do your phone.
To do this, go into iTunes, and tell it to restore your phone. Then when it asks you if you want to restore as a new iPhone or restore from backup, choose “restore as a new iPhone”. This will completely wipe your phone and re-do it from scratch. At that point you can then re-select all items you want to sync and then manual setup your email etc in your phone again. Of course doing this loses any saved settings from before but it’s almost guaranteed to fix your battery drain problem.
This highlights an important item of note – always backup your phone (by choosing “sync” in iTunes), and always keep multiple backups.