For the initial period (about 3 days after purchasing) the 'App Power Monitor' and 'Optimisation Of Battery Usage' features aren’t fully up and running - which is likely why you're getting low battery expectancy readings and others aren't.
To increase battery usage/save power going forwards try:
Repeat any of the above as regularly as needed. Should hopefully stabilise into a better expected battery fairly quickly.
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I am losing 25-30% of my battery OVERNIGHT while my phone is "sleeping". I have Location and wi-fi turned off. Sound and vibration are OFF.and I optimize it before going to bed. Last night it was at 99% when I went to bed, 5 1/2 hours later when I got up it was at 70%. My Note 4 would lose 1, MAYBE 2% overnight. What the heck is going on??? After losing 28% battery life the other day, I recharged to 100% and steadily used the phone for 8 hours . I only lost about 20% while USING the phone. Why the hell is it losing almost 30% without being touched???!!!
I have exactly the same issue as yours. While browsing different forums, one of the members suggested to disable VoLTE. The guy in question had exactly the same problem, 30% to 40% of battery loss overnight.
I have disabled VoLTE right now and I am charging it to 100%, I hope to see a difference. If you want, I'll can keep you updated about it.
Here is the link of the forum : https://forum.xda-developers.com/galaxy-note-8/review/standby-drain-t3647689/page8
I'm coming back at you after trying disabling VoLTE. For me, it worked immediately after disabling the function I noticed a better battery life throughout the day.
I did not charge my phone last night, as it had approximately around 50% of battery. During the night the phone lost only 2-3% of battery in standby mode.
For information, my phone was at 100% yesterday at 2:24 pm and now it is at 42%.
I suggest to check with your carrier if VoLTE is supported by the Note 8 as in my case it wasn't. Here you have a screenshot of my battery usage.
I hope it may help some of you guys.
I had the same problem since I disabled locations this really saved my battery all day at work I listened to music 6 hrs none stop got home at 3:30 battery was on 77% left try this out guy and girls