To Recharge The Battery; To Get The Most From Your Batteries - HP Compaq Presario,Presario 2100 Reference Manual

Note
CAUTION
Once the notebook enters Hibernation in this way, you won't be able to turn it on
again until you restore power by doing one of the following:
Replace the battery with a charged one.
Plug in the AC adapter.
If you plug in the AC adapter, you can continue to work while your battery
recharges.

To recharge the battery

The AC adapter is normally warm whenever plugged into an AC outlet. The
notebook is normally warm while recharging. Don't recharge the notebook in a
briefcase or other confined space, or the battery could overheat.
Plug the AC adapter into the notebook.
To get the longest operating time, wait until the battery charge is below 50 percent
before recharging, and then charge it fully (100 percent). Charging can take
approximately 3 hours. If you continue working while the battery charges, the
charging time may increase.
The operating time for a fully charged battery depends on the notebook model,
power management settings, and level of use.

To get the most from your batteries

Follow these suggestions to make your battery power last as long as possible:
Plug in the AC adapter, especially when using a CD-ROM or DVD drive, or any
external connections such as a PC Card or a modem.
Set the display brightness to the lowest comfortable level (Fn+F1).
Put the notebook in Standby when you are not using it for a short while.
Put the notebook in Hibernation whenever you want to save your current session
but will not be using the notebook for a day or more.
Set the automatic timeout settings to emphasize saving power. If your notebook
has a multispeed processor, use the lower speed on battery power (the default
settings conserve battery power).
Batteries and Power Management
Using Battery Power
Reference Guide 33