Panasonic KX-NCP500 Features Manual page 459

If the DC power is available from backup batteries, even if the AC power fails, the PBX will remain fully
operational.
•
The BRI8 (one PFT port) and BRI4 (one PFT port) cards can also be used for Power Failure Connections.
For details about Power Failure Connections, refer to the Installation Manual.
Installation Manual References
KX-NCP500/KX-NCP1000
3.12.1 Power Failure Connections
KX-TDE100/KX-TDE200
3.2.6 Backup Battery Connection
3.12.1 Power Failure Connections
KX-TDE600
3.2.11 Backup Battery Connection
3.14.1 Power Failure Connections
PC Programming Manual References
13.3 [11-3] Power Failure Transfer
2.4.1 Power Failure Transfer
Feature Guide 459