Location services, push, too much internet, too many games, too many videos, too much porn, too much overall usage, too high of brightness, your phone is broken, too many apps that TRULY run in the background not just sit there, and the list goes on and on and on
1. You're playing a lot of games
2. You're watching a lot of video
3. You have a lot of multitasking going on
4. Location services and push/push notifications are working too often
5. You're browsing the Internet a lot.
Just a thought...when I notice my battery draining faster than normal, I let it drain to almost completely dead, then charge it overnight, and the next day it's usually back to normal. I had the problem recently. I took a 6 hour road trip and by the end of the day, I was down to 20% battery left. I normally have at least 50% left at the end of the day.