Panasonic KX-FG2452CX Service Manual page 57

6.14.4.2. Charge Circuit
Ultra charge (170 mA) of maximum 6 hours is started soon after the Handset is placed on the base unit. Finally the mode
changes to trickle charge (6 mA) to prevent overcharging.
6.14.4.3. Line Sending Signal
Refer to Signal Flowchart in the Whole System (P.54).
6.14.4.4. Line Receiving Signal
Refer to Signal Flowchart in the Whole System (P.54).
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KX-FG2452CX