Did u check the battery saver app for background tasks and disable it?
Also are you running denim or cyan? And did this happen right after an OS update?
Turn off your 3G when you are in a place where you have wifi. Turn of wifi when you need to use 3G. Turning them both on really kills the battery. Also make sure Bluetooth is off and disable gps if you don't use it
Do you have a website pinned on your start screen? This may "always" updating and causes battery usages.
Clear IE history.
What do you mean with battery saver is switched off. You have to look in battery saver if there is an app which had high usages.
Do a soft reset.
If all of this does not work do a hard reset.
What I meant was to check for the app background usage statistics in battery saver.
This will show u the apps that run in the background and might cos a lot of battery drain.
Anyway as said above if there aren't many background tasks then try a soft reset and if it doesn't help then a hard reset should certainly fix it.