Panasonic HDC-HS9 Operating Instructions Manual page 27

To recharge the built-in lithium battery
≥ Connect the AC adaptor or attach the battery
to this unit, and the built-in lithium battery will
be recharged. Leave the unit as it is for approx.
24 hours and the battery will maintain the date
and time for approx. 6 months. (The battery is
still being recharged even if the mode dial is
set to OFF.)
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