I just wanted to record a conclusion to my battery drain issues during phone idle. They were directly related to cell signal. If cell signal was poor the battery would drain at five percent per hour or more when the phone was not used. This was because, I assume, the phone was working trying to get a signal. You could see a strong correlation between cell signal and battery life in the battery graph.
The fix I used, which works well, is switching preferred network mode from LTE/WCDMA/GSM to just WCDMA/GSM. In LTE/WCDMA/GSM mode, the cell radio is doing a lot of work apparently, even if LTE data is not turned on. My cell signal is much better wherever I am located and the phone loses almost no battery at idle. If I need LTE I switch modes temporarily. For reference I am in Philadelphia, Pennsylvania, USA using AT&T on Straight Talk.
I hope this helps someone.