Iphone 6s battery still draining after a battery replacement | IOS 14.0

Hey,

So I have an iPhone 6s with ios 14.0 installed. I had my iPhone with ios 12 and everything was working fine but then I upgraded it to ios 14.0, for 2-3 months the device worked just like it, but in the past few weeks my battery health and degraded and had dropped from 86% to 51% in just two weeks. It was impossible to use the phone without plugging it into the charger every time. Whenever I took out the phone from the charger, it would just shut off within 2-3 minutes of use. So I went to an apple store and told them about my problem. They ran their diagnostic test and it had only reported a battery problem. So I got the battery replaced. Now when I check my battery health, it shows 100% but still my battery is draining 1-2% every 2 mins without even using it. If I watch a 10-minute video on youtube, it drains 6-7% of the battery which is an awful lot. Please suggest what should I do because it's very irritating to see that even after replacing my battery, still, I'm facing these draining issues.