after some months after discovering possible culprit I can by all certainty say that the main reason for draining of the batter on 8" Samsung S2 SM-T713 (Android 7.0) tablet is the sole feature FIND MY DEVICE which you can find Settings\Lock screen and security\Other security settings\Device administrators\ . It is not directly Google Play Store or always sleep. So in order to avoid this drain you need to disable "Find My Device" setting. Please see the photo.
But remember, if you will restart your tablet or your tablet will run out of batter and you will start again this feature will be enabled again so you need to disable "Find My Device" feature again. Sometimes also some update will enable this feature. I discovered this today as I saw that the battery usage graph started to become again very steep (see photo).
I checked "Find my device" setting and yes, of course it was enabled. Just to explain you this graph. I use tablet only for series watching when i travel with train. And you can see normal drain of the battery for the 3 days and decline when i watched my series on train for 3 days. But today you can also see a bit more decline even though I did not used my tablet yet. Tablet was updated with some updates and feature Find My Device was enabled which if I would leave it on would exhaust the battery in few hours.
Question for me is if there is a chance that we can permanently disable "Find My Device" feature?
Best regards and I hope this helped someone with a drain.
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