Let’s get a better handle on what’s happening! Install this gem of an App! [https://www.coconut-flavour.com/coconutbattery/|CoconutBattery] then post a snapshot of the main apps window.
A fresh battery will last as long as what your system was able to before! But without a clean measure there are many reasons why it might appear the systems run time is not as long.
The quality and age of the battery can also skew things.