You should regularly take a moment to check on your iPhone’s battery life. And given how easy Apple made it starting in iOS 11.3, we really have no excuse. All you have to do is hit Settings > Battery > Battery Health, and you’ll be able to see the maximum capacity of your iPhone’s battery, ensure “Optimized Battery…
source https://lifehacker.com/why-your-iphone-battery-is-recalibrating-in-ios-14-5-1846781068