If you have Verizon or in some other models, doesn't seem to be everyone but a good portion of us... in battery usage, have cell standby drain. It's to do with wifi being on.
For example, overnight if I leave wifi in my battery will drain upwards of 20% sitting on my nightstand. If I turn wifi off (or use setting to turn off if asleep) I lose maybe 5% overnight.
Cell standby is "Battery used by cell radio", according to the description in Settings\Battery\Use details. I think its normal for the cell radio to use battery.
I have a Verizon model, and don't see the issue. I turn on WiFi when I get home, and charge the phone overnight.