Why does my battery drain overnight?

[iMore Question]

I've read that switching off the power to my iPhone does little to save power.
But if I simply switch off the lock screen, I lose about 10% of power overnight.
I've tried switching off bluetooth but makes no difference.

 

[Elwaleed Mahmoud]

Check battery usage in settings in the morning to see the real culprit. Also try airplane mode.

 

[Ledsteplin]

Probably push notifications. Email coming in at night will use battery. I keep my phone plugged in a night whether it needs charging or not. That way it uses no battery.