Note 8 battery draining

1)dont keep it on charging entire night
2) close apps which you are not using

open battery usage and check for battery hungry app.
Then uninstall it

Disable sync and Always on display. That will do the trick. And turn off location as well.

As Said, Don't keep for charging whole night. it will be affect your handset battery life.

~Samsung_OS_Developers

I don't charge it overnight.

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search for app that is responsible and make sure that u haven't installed apps from untrusted sources rather than in play store or galaxy store.