Perhaps my solution will resolve your battery drainage. Under settings - gotto Device Care, -> Click on battery, -> Click on battery usage, -> Click on the bar graph (day) that shows the highest battery usage. You should see a list of apps below in order of usage. Now gotto apps, find the app you identified that is using a lot of power. Click on the the app, -> turn off "Allow background activity". What I've leaned is even though you close some applications, they still run in the background. Hope this helps!
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