Sony PCG-GR300 Manual

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To charge the second battery pack 
  Using weight saver for second battery cover 
Keep the battery pack in the notebook while it is connected to AC power. The battery indicator flashes while the battery is
charging. See also "To charge the battery pack" in the printed Quick Start for more information. 
  Charging the second battery 
  Note: 
 
To determine the amount of time the battery lasts, see 
 for details. 
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