Sony PCG-K20P - Manual (Page 53)

Frequently asked questions
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 at all. If you are using a program that prevents the system from entering
Hibernate mode, save your data frequently. Also, see
To activate Hibernate mode for information on how you can manually
activate Hibernate mode.
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