When you're not using your phone overnight, the battery shouldn't be tanking. A properly-optimized phone should only lose 2-7% battery overnight, but if you're waking up to see your phone having gone down 8% or more, there's something wrong with your settings and there are things you can do to significantly improve overnight battery drain if you aren't plugging in each night.
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Your phone should barely lose battery overnight — if it does, check these things
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