iPhone 6S battery excessively draining

Hello,

My iPhone 6S battery drains really quickly and I constantly need to put it in a charger just for it to work. I have an iPhone 11 Pro Max and a Samsung Galaxy S20 Ultra 5G, and since these batteries are over 4000 mAh, I am able to use it for a full day and those batteries are still at at least 20-30 percent. However, for the iPhone 6S on iOS 13.5.1, after even a full charge, when I start playing a random game like Homescapes, Gardenscapes, or even Wordscapes for a period of time (30 minutes), it drains rapidly from 100 to 10 percent. My battery health is at 82 percent, while my iPhone 11 Pro Max is at 98 percent as of 24 June 2020. Even though one of my iPhone 4's batteries doesn't drain that fast (it only drains from 80 to 75 in 10 minutes), my iPhone 6S drains really quickly, even though iOS 13 is meant for battery optimisation. Sometimes in the restroom during a shower when I leave the phone on the photos app looking at a picture of a sky (doesn't consume much battery since it does not consume much power) at full brightness, it sometimes drains from 50 to 10 percent after only 10-15 minutes, which is totally shocking. I have scheduled an appointment, and also, sometimes, when I try to type something, sometimes the right side of the touchscreen doesn't work so it takes a long time to type some basic text out, and plus, the touchscreen sometimes glitches, even though the phone is not cracked (it was 3 years ago, when my Chinese girlfriend dropped the phone by accident after I decided to give the phone to her).