Iphone 6 battery drain
my iphone 6 not lasting even 4 hours on standby losing 5 - 7 % overnight with all the apps closed from 100 % drops to 70 with 1 hour usage on web browsing
iPhone 6, iOS 8.2
Probably apps running in the background are causing this, sometimes Mail get's stuck connecting to the mail server, or some social media app like Facebook can also be a reason for prolonged background activity.
Try to reset the phone by holding the sleep and home button for about 10sec, until the Apple logo comes back again. You will not lose any data by resetting, but it can cure some glitches.
If this does not help, setting it up as new device would be the next step:
How to erase your iOS device and then set it up as a new device or restore it from backups
Maybe also take a look at this page about battery drainage