I have installed the iOS 14 on my iPhone 6s plus and the battery drains pretty fast. After analysis I got root cause and solution for battery drain issue. Root cause of battery drain and temperature high issue due to wifi and bluetooth bug. Solution: Below steps need to perform to fix ios 14 battery drain issue on iphone. 1) Reset network settings. Settings-->General-->Reset-->Reset Network Settings 2) WIFI off Settiings--> WI-FI--> off 3) Bluetooth off Settings--> Bluetooth--> off After performing these steps my battery drain and temperature high issue have been resolved. Battery performance back to normal. Please do from ur end hopefully issue will be fix.