i do not normally try to answer iPhone questions, but because you originally posted in the Technology forum, I figured I would offer what I know, and get you moved to the iPhone forum.
If you have a poor signal, it can cause the iPhone to increase the radio power to maintain a connection.
If your carrier supports Settings -> Phone -> Wi-Fi Calling, this might help keep the iPhone from worrying about maintaining a cellular signal (I'm guessing actually).
With Apple selling millions of iPhones, there is always a statistical possibility for a bad battery to slip into the mix. So if you think you have a bad battery, you should see about making a Genius Bar appointment at your nearest Apple Store.
Now maybe someone else will have an idea of what might be draining your battery life over night.