Sony VGN-FS550 - Manual (Page 145)

Can my computer enter Hibernate mode while using battery power?
Your computer can enter Hibernate mode while using battery power, but some software programs and peripheral devices
prevent the system from entering Hibernate mode. If you are using a program that prevents the system from entering
Hibernate mode, save your data frequently to avoid losing data. See
To activate Hibernate mode for information on how
you can manually activate Hibernate mode.
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