Siemens S6 Power Service Manual page 18

Private Communication Systems
Mobile Phones
* Plug the battery into the desktop charger.
or
* Apply +5 Volts between the BATT+ and GND contacts (see drawing!)
Limit the current to 10mA.
Deep Discharge
If the battery is deeply discharged it can be recharged by the following procedure:
Insert flat battery into handset and connect travel charger. The charging symbol will
not be visible. Wait for appr. 1 hour and disconnect charger afterwards.
Remove battery and reinsert it. If you connect the travel charger now, the charging
symbol must be visible on the handset display.
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