I'm seeing similar issues (see post "erratic battery life..."
http://forums.androidcentral.com/sa...now-since-upgrading-nougat-2.html#post5808335). Mine started the week
before the N update hit my phone. I'll have several days of good performance, and then I'll see the battery tank overnight, like it did last night. A few times this has happened during waking hours, and my phone has always been very hot associated with these drops. Got my phone on 25th November 2016, so not very old to me. Close to having US Cellular order me a refurbished unit, since cache wipe, FDR, SIM change have not resolved the issue.
Just downloaded GSAM, have been using Samsung battery app. Will see what GSAM might indicate as the problem. Usually my big hitter is Android System