Sony VAIO VAIO PCG505F User Manual page 21

You can use a battery pack as a source of power. The PCGA-BP51 battery
pack that comes with your computer is not fully charged at the time of
purchase. Follow the steps below to insert and charge the battery pack.
Move the lock lever on the bottom of the computer to the
position.
Align the grooves and tabs on the battery with the tabs and notches
on the back of the computer, and then slide the battery towards the
computer until it clicks into place.
Slide the lock lever into the
computer.
position to secure the battery on the