Panasonic KX-TGM420 Operating Instructions Manual page 195

Charge only mode
The charge only mode is the dedicated mode to charge
the backup batteries of the base unit. Do not use this
mode if it is unnecessary because all functions except
the base unit's battery charge is disabled with this
feature on. Leave all the registered handsets on the
chargers during use of the charge only mode.

To activate the charge only mode:
1 Press [ANSWER ON/OFF] to turn on the
answering system.
• Make sure the message counter turns on.
2
Disconnect the telephone line cord, the AC adaptor
plug, and remove the batteries from the base unit.
3 Press and hold [
same time, then insert the AC adaptor plug to the
base unit. Keep on pressing these keys until a
beep tone sounds.
4
Release these keys.
• The message counter turns off.

], [ ], and [ERASE] at the
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