I often think of the battery in my notebook as a mobile UPS (uniteruptable power supply - not the parcel company), partly in that I try not to depend on it if at all possible. If there is the slightest hint of an available power socket I'll take my power supply along with me.

There are some times when there is no choice but to rely on the battery and it is worth spending a little time getting to know your notebook and how to save power. For example my main notebook has a keyboard shortcut to turn wireless off. Annoyingly, whilst this can be done at any time in Windows, Ubuntu doesn't react to the key. Score one to Windows there.

Armelle O'Neal at Microsoft came up with a helpful list of tips for lengthening battery life. Well worth a read, even though it is focused on Windows XP.