To make the battery last longer, you could:
Set the HDD to power down after 10 minutes or less of non-use.
Set the screen to turn off after 1 minute of non-use in place of the screen saver.
Set the system to hibernate rather than sleep when the lid is closed. Hibernation saves the current window session to the HDD rather than memory, and does not use power to keep those settings.
Set the screen to the lowest but still readable setting.
It is recommended:
DO NOT keep the battery on AC power ALL of the time.
Most of the time only let the battery drain down to 30%-25% then put it back on charge. Let the battery charge back up to 100% and unplug. About once a month let the battery drain completely.
It is suggested that you plug your computer into an outlet when using the following:
CD/DVD drive
External USB devices; drives, mice, or other self powered devices
Editing/Rendering, PowerPoint with video and sound, Movie Maker
Playing games or music that constantly access the hard drive.