HP Notebook Series Reference Manual page 81

If the Time Remaining for the Battery Pack Is Not
Correct
The Time Remaining is an estimate, not a precise value, and is
based on the rate at which the notebook is using power at the
moment. This value therefore depends on your current task and
assumes that you will continue using power at the same rate until
the battery pack runs out. So, if you check the Time Remaining
while the notebook is performing a task requiring a good deal of
power (such as reading from a CD or DVD), the value will
probably show less time remaining than you really have, since
you will probably later switch to tasks that require less power.
If the Notebook Does Not Enter Standby Mode as
Expected
If you have a connection to another computer, the notebook
will not enter Standby if the connection is active.
If the notebook is performing an operation, it normally waits
for the operation to finish before going into Standby.
If the Notebook Does Not Enter Hibernation as
Expected
Make sure Hibernation support is enabled. From Control
Panel, open Power Options, then select the Hibernate tab.
Check the Power Schemes tab. Make sure the Hibernation
timeouts for both AC power and battery power are not set
to Never.
Reference Guide
Troubleshooting
6–17