I have the same - iPhone 7, on iOS 14.4.2... previously I saw the Fitbit app would run in background overnight, I thought it was this. I have now changed location services to only run while using and turned background app refresh off. But last night went to bed with no apps open, battery at 86%... wake up 7 hours later to a battery at 46%, check battery usage and nothing shown as running whilst I was asleep - so what is draining the battery? Are apply going to pay us all for new batteries as this level of drainage will be degrading the battery faster than it normally would do!