Panasonic KX-TGM420 Operating Instructions Manual page 28

Handset battery charging
2 rechargeable Ni-MH batteries are installed in the
handset at the time of shipment.
Before initial use: Remove the yellow insulation
sheet before using the handset.
Charge for about 7 hours.
• Confirm "Charging" is displayed (A).
• When the batteries are fully charged, "Fully
charged" is displayed.
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