Battery drains within half a day (phone always „awake“)

What really bugs me is the way the battery usage can mysteriously speed up overnight. For instance, last night before going to bed the Settings told me I had 12 hours left on the battery. It went flat in less than 6 and I missed my alarm call.

IMVHO it seems to me to be a failing of the Fairphone that it has to remain on all night to work as an alarm clock. Whereas with my old Nokia I could set the alarm and switch it off, and it would automatically switch on with the alarm.

I don’t know how to reproduce the battery usage chart here, but here are the stats:
Screen 10%
Wi-Fi 9%
Email 8% (this is the generic app, which I have abandoned in favour of Outlook: Emails from Fairphone haven’t been sent )
Phone idle 3%
Google Services 1%
Mobile standby 1%
Android OS 1%
…which leaves 67% unaccounted for!