no mobile coverage drains battery

Where I live I don't get cellular coverage at all, but my iPhone 5's battery is draining 80% overnight with no background apps open, no nothing running, it's just this 'No Mobile Coverage' service that is draining my battery but I can't do anything about the no signal where I live so how can I stop my iPhone from trying to constantly connect to something it can't? Battery is literally dead in 2-3 hours after full charge. I use an app from my network provider so I can text and make calls using wifi and the phone works fine when I'm in places with cellular signal and my battery doesn't get drained, it's only when I'm home and have no signal. So is there an off switch for this stupid 'No Mobile Coverage' thing???