I sure noticed it the past few nights. Usually I have my phone on charger as I sleep, I had to set it for a 6am alarm yesterday and this morning. With 100% charge last night at 12:30am'ish, my battery was down to 83% yesterday morning, 74% THIS morning. Screen off, no apps running.
Looking at Battery activity, it seems Dropbox is running in the background all night at various % rates! I have that app background refresh off. I started noticing this crazy battery drain when I was out on Sat. Not much use with my phone, but in the span of just 2 hours I was down to 69%.
Extremely not normal. I updated to 13.1.5...skipped the previous 2 updates after seeing some other issues on here.
In the past when I left it off my charger I may lose 4-5% at the most overnight, 6-7 hours. (Battery health shows "95%") SMH