Sony PCG-XG28 Primary User Manual page 67

Keep the battery pack in the computer while it is connected to AC power.
The battery indicator flashes while the battery is charging. See "To charge
the battery pack" on page 15 for more information.
There is a RELEASE lever on the bottom of the weight saver. To
remove the battery pack, slide the RELEASE lever on the bottom of
the computer in the direction of the arrow. See also "To remove the
floppy disk drive (Windows 98 models)" on page 32.