I installed iOS 14 on my iPhone 6s when it was available. The battery went from 98% to 45% in about 2 minutes as I looked on. A minute later, it was under 20%. Then, charged overnight, but never reached 100%. It stopped around 94% (1st time ever). Unplugged and saw the percentage drop like a comet. I didn't even have time to use the phone when it dropped under 20%. Placed in charger again and it took hours longer than normal. A third time the percentage dropped, I turned off the phone and searched online on my PC about going back to 13.7.
Thankfully, there was an Apple download available.
Now, at iOS 13.7, the battery lasts all day and more (I am a light user).
The only unimportant issue is that I have 2 notices in settings that won't go away. One says I cannot backup because a "newer" backup is present (due to the iOS 14). No sweat. The other is saying a new version is ready (Oct 20, 14.1).
I will wait for 14.2, 14.3 or whatever fixes this.
It SHOCKS me that Apple is not addressing the widespread battery problem.
If all else fails, I will stay with 13.7.