I didn't see any mention of u restoring the device in Recovery, then setting the device up as a new iPhone without adding any third party apps. U did say u restored it in DFU and restored the backup. Maybe I'm wrong, but I don't remember u saying u ever tested it as s brand new iPhone. I do remeber reading u saying that u want Apple Support to resolve the issue with ur backup restored. As much as u might not want to, and as much as u believe the issue is iPhone software, the likelihood is that ur issue is caused by a third party. If u restore ur device in Recovery Mode, and u still have battery issues, AppleCare will repair or replace the device.