When an HP computer has a problem it beeps at you. At first it sounds concerning... and not all beeping is bad... but this is how the computer lets you know what's happenin.
All manufaturers of hardware have some way of communicating to what is going on... especially when there is a problem. Just like routers use lights, HP and others use beeping.
When you boot up your HP computer and it beeps 9 times... once every second... pauses for two seconds... then does it again... the trusty old computer is telling you that the battery is DEAD!