So about 4 mins worth is about 1GB.
I've had iOS11 GM installed on my phone for a week now, and my battery is noticeably worse. I don't know what to tell you.
Housekeeping period is over and my 6S drains like crazy.
It's an old battery by now, but it wasn't this bad on 10.3.3.
My iPad Air 2 seems fine though.