It does depend what have you done with the phone. People have used phones as hotspots 24/7 with charging all the times. Or used them to farm ads money 24/7.
Most likely its just some app you installed that is consuming battery. Google services and apps are biggest drainers.
I did use my old phone as hotspot when i was in college back in 2011 when i had unlimited data....
Some software updates might cause it also, have had issues with that before, phone drains like crazy.
Now i just install Cyanogen OS on my phones. New or old, doesn't matter. For example my Oneplus 5T Pro last only 5-6 hours SOT after firmware update, installed Cyanogen, 4 days and 13hours with 13h 25mins Screen On Time.