After updated iOS 14.7.1, my iPhone encountered severe battery drain over night, dropping almost 60-70% battery. Tried to disable all kinds of background activity: Siri, Find my phone, Email, Music, …, nothing worked. The battery graph showed nothing was going on during the night, but still drained like a slant slope. The battery health even hit 79%, indicating need for replacement service.
The almighty Google of one thread in Apple forum finally saved my phone from a week of battery pain: Resetting the network. Yes, after that, one night just takes 5% the juice.
Update: Also encounter problem unable to charge after the iPhone 13 event. Turns out that some dust stuck in the plug hole prevents the charging. Brush it out with a long brush (toothbrush is not deep enough), then charging will work normally.