Welp.... based on the above I decided to give the update a shot and it just destroyed my battery life. Just last week, with Nougat, the phone was lasting 2-3 days of semi-light usage. I was used to finding the phone all the time holding on to life for quite a while even with 1-3% remaining. Now, it doesn't even last close to a full day with ZERO usage: I charge the phone and turn it on, put it down, and come back ~18 hours later to find it already dead.
I am now trying to run it with wifi disabled (but mobile data still on). So far it seems to be doing much better, at least right now it's only down to 90% after being on (and idle) for almost 7 hours. Obviously not a real solution, but it does show that it seems to be caused by wifi.
I haven't installed any apps, nor rooted or even flashed TWRP since flashing the RUU -- everything is "stock." Speaking of which, did you guys without this problem install the RUU, or the OTA update? I wonder if this could be a problem with the RUU only?
Has anyone successfully downgraded back to Nougat? *I just tried the 2.51.617.32 zip and it says "FAIL12 RU_ZIP_ERROR"