High battery usage with data on

Last week, my Sony Xperia started to rapidly lose battery (30% in one hour). Following the handy advice from other threads; I deleted recent apps and stopped Google auto backup, no luck.
What's worked is turning off the data/ wifi, I'm guessing it has something to do with an app trying to update itself and getting stuck? Any ideas how I can tell which app is causing the problem?
Battery usage blames "Android System" for 50% battery usage, but guess it's another app requesting info from Android?

Thank you for everyone's help, hope this question hasn't already been covered!

"Android System" is most of the phone, including updating apps.

If you've moved any apps to the SD card, move them back to the phone, turn the phone off, and remove the SD card. Then see if it still happens. (An app moved to the SD card can damage the card, causing a file to be looped, which would cause the file, if it was part of a moved app, to "update" forever, eating a lot of battery.)

Hiya, this is the original poster. (just set up a profile)
No luck with the sim card idea. Restarted and took the card out, battery usage still much higher on data than off. Any ideas about what else it could be?
Thanks!