Depends on what you were doing with your phone really, and if it was any different than usual. Also, you've got to remember that every time you bring down the notification center, it reloads the widgets, so if you've got a lot of stocks or you're checking it often; it'll use more.
Could also be Diagnostics & Usage. Settings -> General -> About -> Diagnostics & Usage -> press Don't Send.
I remember hearing about that using data and causing excess battery drain.