[deleted] I forgot to tell you that you should check "Media Server" in morning. Because when you are not using your phone for long duration(e.g. in night) then it is best time to check your idle battery drain.
I think some apps or system service draining the battery.
You should install accubattery (with network permission off and also give it usage access). Before sleeping, note down your battery percentage, take screenshot of battery usage. In morning, take screenshot of battery usage in settings as well as in accubattery. Keep it doing for 4-5 days and compare which app & service was active during night.
Here is the all the different combination before going to bed you can use (I am assuming that you still have play services installed):
1st time, reboot the phone and enter the password so that app & services will autostart. Wi-Fi & mobile data OFF if possible keep aeroplane mode ON.
2nd time, reboot the phone and enter the password. Wi-Fi or Mobile Data ON.
Compare the usage of both days
3rd time, don't reboot the phone. Wi-Fi & mobile data OFF.
4th time, same setup as third one but keep Wi-Fi or Mobile Data ON.
Compare the battery usage.
It will give you rough idea which app or services causing problem. 8% idle battery drain for (assuming 8 hrs) means you are losing approx 24% battery in 24 hrs without using your device.
I think i am looking stupid by writing this type of thing on a technical discussion forum 😥.