What is the point of Hardwired power for Doorbell 3?

Hello. I recently installed a Ring Doorbell 3 and added a hardwired power supply. The app confirms power is now Hardwired. The question I have is that the battery was at 99% and it has still drained to 94% in a day. Is this normal? I am confused. Why is it discharging so when connected to an external power supply? I feel, I might as well not have bothered. These forums seem awash with issues regarding hardwiring the power but no one seems to explain what the issue is.