Panasonic KX-TD500 System Reference Manual page 1436

3.15 CPU RAM backup battery down
Error Code
Possible cause of
the malfunction
Countermeasures
Note
0C00
1) Defective rechargeable lithium battery on the CPU card
2) Defective CPU card
After replacing lithium battery,
turn on the POWER switch
Is there a new related error mes-
sage in the Error Log?
Yes
*1. Consult the nearest service center
*2. It is recommended to have a current copy of the program on disk or tape
to facilitate accurate and rapid recovery.
*2
Replace the CPU card
Enter the system data
End
15-E-18
*1
No