Sony PCG-GR300 Manual

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To remove the second battery pack 
If you attach two battery packs, you can remove either of them without shutting down the notebook. When removing one
battery pack, make sure that the other battery pack's indicator is on. If the indicator of the battery pack you are removing is
on, right-click the battery icon on the taskbar and click the "Switch discharge battery" option. 
1.
To remove the battery pack, first slide the multipurpose bay Release lever in the direction of the arrow to unlock
the weight saver. 
  Multipurpose bay Release lever 
2.
Remove the weight saver, and then pull out the battery pack. 
3.
 for more information. 
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