how long does macbook pro battery long?

It varies quite aa bit depending on year, configuration, apps, etc.

See: About Mac notebook batteries - Apple Support

I have the same question, on September of last year, Apple replaced my 11m old pro MacBook Pro with the 2019 version w/ the touch bar after I have sent my original one to get the battery replaced and it was lost. I only use the computer to do school assigments and I have the feeling the battery is not lasting again. I started to use the computer at 11:02pm with a 95% charge, at 0:03 am it was at 34% but in the system says the battery is functioning normally, just like my previous MBP.