Battery will drop from 80% to 40% within 30 minutes even when it not being used

I just got a new Iphone 11 last December. Within the last week, my battery has started acting strange. It does not keep a charge nearly as long as it used to. For example, it will drop from 80% to 40% within 30 minutes even when it not being used. Is there anything I can do to help this problem?

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