VTech VS150 TWIN User Manual page 38

Power-fail backup mode operation
During power-fail backup mode, the telephone base, answering
system and sensor alert system will be disabled. The operating
time is subject to the battery level of the handset placed in the
telephone base and the actual usage. For optimal performance,
you are not recommended to use the handset placed in the
telephone base when this mode is on.
Using other system handsets (Recommended):
Operate the handsets the same way as usual, except the answering
system and sensor alert system which will be disabled.
Using the handset placed in the telephone base:
To maximize the operating time, you are not advised to use this
handset. If you do have to use it, make sure you do not lift it from
the telephone base. All operations should be done with the handset
placed in the telephone base. In this case, calls can only be made
and received using the speakerphone.
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