If the power supply to the PBX fails, specific single line telephones (SLTs) are automatically connected to specific outside (CO) lines (Power Failure Connections). The PBX will switch from the current connections to Power Failure Connections, and all existing conversations will be disconnected.
Only outside (CO) line calls handled by Power Failure Connections can be made during a power failure.

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During a power failure, each of the following outside (CO) lines will be connected to an assigned extension.

Outside (CO) line 1: extension jack 01

Outside (CO) line 4: extension jack 09

Outside (CO) line 7: extension jack 17

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Only outside (CO) line calls are possible during a power failure. All other features will not function.

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We recommend connecting an SLT in parallel at extension jacks 01, 09, and 17, so that the SLT can be used during a power failure.

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Automobile-type batteries, which must be user-supplied, can be connected as a system backup power supply to operate all the features during a power failure.
The batteries can be connected directly to the unit with optional cables. For more information, refer to the Installation Manual.

•	In the event of a power failure, PBX memory is protected by a factory-installed lithium battery. There is no memory loss except the memories of Automatic Callback Busy ( 1.7.1 Automatic Callback Busy (Camp-on)), Call Park ( 1.12.2 Call Park), and Redial ( 1.6.1.4 Redial ).

•	2.2.6 Connecting Backup Batteries
•	2.9 Power Failure Connections