A few weeks ago I noted the same thing. Thought my extended battery was failing so replaced it - and no difference. Finally downloaded an app called A Better Battery. This helped me track it down to an app that I had updated. I could do without it so I removed it, and that resolved the issue. The reason other apps couldn't help is that the offending app was an active wallpaper which triggered 10%+ per hour drain attributed to the OS.
A Better Battery has a neat feature that shows average hourly burn rate - should tell you if you've got a problem. On my phone I see 4-6% per hour when it is working normally. With excellent coverage it can get down to 2-3% per hour. Anything over 6% and I look for a problem, or just reboot.
As others stated, could be apps, could be spotty coverage. I've also had a runaway Email app and runaway bluetooth. First thing I do if I'm seeing a big power drop is to reboot, which usually clears it up.