Compaq Presario,Presario 1211 Supplementary Manual page 86

Once your Notebook has
entered Hibernation mode, it
will not turn on until it is
plugged into an AC adapter or
the drained battery is replaced
with a charged one.
A low-battery condition exists when the battery has less than
10 percent of its power remaining. This section of "Caring for
Your Battery" will show you how to correct a low-battery
condition and what to do if your Notebook loses all battery
power.
When your Notebook loses all
battery power, it begins
Hibernation, a process that
cannot be interrupted. If
Hibernation has begun, you must
allow your Notebook to finish
saving your information and shut
off automatically before trying to
correct the low-battery
condition.
The availability of an AC wall outlet will determine which
solution you should use to correct a low-battery condition.
Use one of the following options:
This solution allows you to continue working without being
interrupted and simultaneously charges the drained battery.
You don't have to turn off your Notebook before connecting
the AC adapter. Your Notebook automatically switches to AC
power once you connect the AC adapter.