Battery Drainage while not in use.

Well, last week, my iPhone 5s was working perfectly. Working 12-hour shifts while listening to podcasts in airplane mode would make the battery go from 100% to 92% by the end of shift.

THIS week, the thing drains badly. Five minutes after unplugging it, it loses 5%, and keeps going down.

Last night at work, I went to plug it in while it was reading 70%. As soon as I plugged it in, it instantly dropped from 70% to 57%. I've never seen that happen before.

My Wife has the same model as mine, and she's not experiencing this issue.

I've stopped location services and a whole bunch of other stuff. Bluetooth is off as well.

I'm wondering if there's some hidden background program running to cause this, or a faulty battery.

Any help would be appreciated.