I had the same issue in my data center. Old Dell PowerEdge 1950 servers started to generate this alarm.
Only the servers with a separate dedicated battery to for RAID controller where generating this alarm.
So in my case this was NOT a ghost alarm, it was very real.
The battery in question is connected to the RAID controller to keep the memory modules alive for RAID while its moving data back and forth between the drives.
This batteries do have a finite life span and eventually they do stop charging.
The PE 1950 without the separate RAID card installed (and no separate battery) did not had this issue. All my PE1950 where made in the same year.
SOLUTION... in my case was to buy the new battery, shut the host down, replace the battery, restart the host, Acknowledge the alarm, reset it, and that's it.
Once I replaced the battery in two of my old PE1950 - alarms stopped.
Hope this helped.
The Battery you want to replace sitting next to the RAID card in the left corner of the server (PE 1950) close to the front panel, near by the power button. Battery kind of large, inclosed in the black plastic, resembling old fat cell phone batteries.