Stand by battery usage

It depends on three factors:

1. If it is in standby, but not in airplane mode, it can make activities (like receiving text, whatsapp, other apps messages) and/or checking for cellular/wifi network , and/or downloading some updates, backing up, etc. If so it can lose 2-5 level percentage per hour)
2. If it is in airplane mode, without wifi enabled, it should use 3-6 level points in 8 hours.
3. If the battery is close to the critical point of its life (Settings>Battery>Battery Health>Maximum Capacity = 83-80%), it can have unpredictable behavior and use much more level points.

Regards

Giulio