"No Cell Coverage" drains battery overnight while charging

My house is in an area where the cell coverage stops at the curb and does not reach my home. I use wifi calling inside the house. When I plug my phone in to charge at bedtime somewhere in the night "no cell coverage" starts pinging for a tower to talk to and even though the phone is plugged into a charger it drains the battery. I've read all the articles on the web that say put the phone into airplane mode, and I created an automation that did just that but the battery still drains. I added turning off cell data to the automation and STILL the battery drains. For the record, this is an iPhone 11 and the battery itself says its max capacity is 86%. The odd thing is that it doesn't do this EVERY night...just about 5 out of 7 nights per week. Oh, and one more thing, when I wake up and see the battery is almost drained I get my morning coffee and plug the phone into my iMac and low and behold it charges...this only happens at night! Grrrrrr!

Does Apple have any suggestions that "work" to solve this? Is there some way with automation I can kill "no cell coverage" when it tries to run in the night?