For those who said that battery drain alot during night time is actually very subjective.
Why did i say so? There will be 2 scenario.
Scenario 1 my own Note 5.
Basically my own phone drop battery around 1 to 2% over the whole night where normally i sleep 6 to 8 hours.
How do i preserve this constant drop percentage?
Before sleep, normally i will pick up my phone and press the multitask button and close all applications. Thus i will go to smart manager app to press the clean all button and then only let the phone sleep.
Thus for Note 5 battery don`t always cultivate the habit of charging even the battery % is still high. Use until left 15% and below only charge. Sometimes i use until left 3 to 5% then only charge.
My phone is already 4 month old and according to the Samsung Phone Info Software so far i only charged my phone 129 times.
Scenario 2 other people Note 5.
Basically if the battery drop fast over night got many possibilities.
1. Battery it self got issue.
2. Motherboard leak battery.
3. Where Software Application runs alot in background.
+++ Many others reason where contributed to the possibilities.
Last but not least, i wont say that my perception is 100% true. Generally how battery % drop is decided by how user use their own phone. These subject of battery reduction over time is very very subjective where no body could measure how, why and when.
None the less, my SOT time i always get in between 4.30 hours to 5.30 hours depends on how i toggle with the brightness and how often i use mobile data and GPS / Location.
A gentle reminder. If you think that the battery drop unusual, please monitor it a few more time. If and only if it happen constantly then send your phone to Samsung SC they can help to check because Technician will always have their own sets of method.
Cheers

agree with you,if close all the apps and clear the ram before sleep thn the phone probably wont drain much battery
but i think most of us wont do that,some of them even telling you that it shouldn't be like this