Sony PCG-XG28 Primary User Manual page 27

Connect the AC adapter to the computer.
Insert the battery pack.
The computer automatically charges the battery (the battery indicator
light flashes in a double blink pattern as the battery charges). When the
battery is 85% full, the battery indicator light turns off. This process takes
approximately two hours. To charge the battery completely, continue
charging for an additional hour. See "Displaying Detailed Battery
Information" in the online manual Customizing Your V AIO® Notebook.
There are two battery indicator lights on the computer:
On
Single blink
Double blink
Off
Indicates the status of the battery pack in the battery bay
on the left side of the computer.
Indicates the status of the battery pack in the drive bay on
the right side of the computer.
The computer is using battery power.
When BOTH the Battery indicator and Power indicator
single-blink, the battery is running out of power.
The battery is charging.
The computer is using AC power.