battery health

Batteries degrade over time with usage due to chemical aging, that's just how they work.

You can expect about a 1% drop per month with average use on an iPhone.

Apple recommends replacing it when it reaches 80%.

iPhone Battery Replacement.

iPhone Battery Repair & Replacement - Apple Support

About Lithium Ion Batteries

iPhone Battery and Performance - Apple Support (IN)

Here are some tips on maximizing battery life.

Batteries - Maximizing Performance - Apple Batteries - Maximizing Performance - Apple

Apple does not sell iPhone 11 anymore. Where did you buy this device from? When did you buy it? What is the current battery Capacity?

Without the above info, it is hard even to guess the situation that you are in.

It would be better if you can please re-post with a screenshot of current Battery Capacity, in order to understand the phenomenon better. Images/pictures speak louder than words. 

Please understand this is a public forum: While attaching a Screenshot, do not provide any personal credentials, such as IP address, Card detail, email id, apple id, IMEI number, Serial Number, Phone number, Order ID, if you are sharing a map ensure your location is not identifiable, etc.

I am having the same issuse now on my 13 pro in may16 it was on 95% now on 29 its 94 it’s decreasing like this in a fast way it was on 98% but it has suddenly been dropping does anyone know how to fix this?