Diagnostic say no issue but battery is constantly running

Hi,

Following document could help your question.

Get help with your Mac notebook battery - Apple Support

You may have a software issue that is causing your laptop to work hard thereby heating it up and causing the fans to run at high speed. Run EtreCheck and post the report here using the "Additional Text" icon which looks like a piece of paper.

Unless the Battery Condition is "Service Battery" or "Replace Soon", or the Apple Diagnostic reports a battery fault, or the battery run-time is too short, or the battery is swollen, then it is time to replace the battery, otherwise you battery is probably Ok. Unfortunately with macOS 11.x has changed the reporting of the battery condition so it is impossible to know its real condition (I don't know if Coconut Battery can still report a battery's true condition).