I always turn off the chassis intrusion feature from the BIOS, myself. In my experience, a weak battery either throws its own error (right approach) or the clock suddenly doesn’t keep good time, at least on boot.
Chassis intrusion means a Chines or Russian spy has entered your pc.
I guessed it when you said you had unplugged it.
Years ago these batteries needed changing every few years.
I was tempted to turn it off too, but after reading this I thought the battery change may be better to try at first. After all, if it was a weak battery, I thought it would need to be changed anyway at some point.