apple pencil battery life

I have an iPhone 8 and updated it to iOS 14.1 when the update came out, all was good for the first week or so and now my battery health has gone from 91% to 50%! I’ll charge my phone and it will decrease in barters percentage drastically just by using it for 10 minutes (eg. Start on 75% and after 10 minutes of use go down to 23%) I can barely use my phone without it being on charge now. It also keeps shutting off while on 20-40% even though it’s not dead? It’s even died on me at 67% which is beyond ridiculous. Needless to say this is the last iPhone I plan on owning, just wondering if anyone else has been experiencing the same issues?

I talked with Apple Support, and they think that iOS 12 may not recognize the Apple Pencil. The iPad Pro sees the device and charges, but doesn't write. Any ideas?

I want to use Apple Pencil in Safari via pointerEvents, but it seems not working properly. Sometimes it does not fire pointer event when I tapped rapidly. I found similar issue in here - https://stackoverflow.com/questions/64314226/ipados-14-apple-pencil-fast-tapping-not-working-html-javascript-ontouchstart/64316781#64316781 and using touch event seems workaround this, but I'm confused this is a bug or intended. If it's intended, how to detect Apple Pencil via touch(or pointer) event? Or is there any solution without these events? Thanks.

Hey, how long it takes to power the battery for iPhone 6 Plus if the battery is charged to 100%

Apple pencil force calculation doc:https://developer.apple.com/documentation/uikit/touches_presses_and_gestures/handling_stylus_based_input/computing_the_perpendicular_force_of_a_stylus,indicates a division of a measured force by the sine of the attitude angle. Shouldn't this be multiplication?Thanks in advance