Panasonic KX-TGM420 Operating Instructions Manual page 33

Base unit backup batteries
2 rechargeable Ni-MH batteries are installed in the
base unit at the time of shipment. These batteries can
be used to supply power to the base unit in the event
of a power failure.
Before initial use: Remove the yellow insulation
sheet before using the base unit.
Base unit battery status when a power failure
occurs
Item
*1 When the base unit is running on battery power,
" " is displayed on the message counter of the
base unit. If there is other information that can be
displayed, such as the number of answering
system messages, the other information is
displayed.
Battery Status
Power backup mode is on.*1
Battery power is low.*2
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