Notebook battery discharges when I plugin connector

[starLED]

I have an older Acer notebook with a battery of 60% capacity health.

When the battery is 20% or less remaining, if I plugin adapter connector without adapter being plugged into wall socket, the battery discharges immediately to 0% and notebook shuts off.

Why is this happening?
Is this potentially dangerous to the notebook?

 

[aliarifat794]

The power management system in your laptop might be malfunctioning.

 

[starLED]

It happens also when the laptop is in sleep mode with 20% battery or less, and after plugin in connector and wakeup it shows 0%, meaning it discharged while not powered on.

 

[tonyfi]

Your battery likely has unstable voltage due to aging cells. When critically low (20%), plugging in a 'dummy' adapter (not connected to power) confuses the power circuit, triggering immediate shutdown as a safety measure. While not directly dangerous to hardware, repeated sudden shutdowns risk data loss/corruption. Consider replacing the battery or always ensuring the charger is properly powered when connecting.

 

[starLED]

Yes, you are right.
Fortunately, laptop does go into hibernation mode when that happens, so it doesn't shut off abruptly.
I will look for a new battery.