Actuallly i am using iphone xr and i have faced so mamy issues after installing ios 14, actually it used to last for few hours and the health app used to keep on running in the background and it took nearly 6.5 gb of internal storage for no reason. So, I have deleted entire dats in my phone, go to settings and press erase all contents and settings. then updated to 14.0.1 no it is back to normal, the battery backup is gud. so please follow the above method and dont restore ur iphone from prev backup, install everything newly and u will find the change in battery life for sure.