Panasonic KX-TD500 User Manual page 249

Problem
A Power Failure occurred.
Appendix
When a power failure occurs...
The system and Panasonic Proprietary Telephones stop
all functions. Specific extensions are automatically
connected straight to specific CO lines. This provides CO
line conversations between the pre-assigned extensions
and CO lines:
Consult your dealer for detailed information.
All intercom calls and features do not function.
When turning the power back on...
Your system restarts with the stored data automatically.
Memory is protected by a pre-installed lithium battery.
There is no memory loss except for Automatic Callback
Busy (Reserving a busy line) and Held calls.
5.1 Troubleshooting
Remedy
249