Does Ubuntu lengthens battery life?

By "battery life" do you mean "the amount of time the system can run off a battery" or do you mean "the length of time before the battery refuses to hold a charge"?

I don't believe Ubuntu does anything specifically to lengthen battery life (using either definition) however the usual measures recommend by the battery manufacturer are often best followed and are usually not specific to one operating system or another.

By battery life, I meant 'the amount of time the system can run off a fully-charged battery'.

In fact, I was asking about Ubuntu's power consumption as compared to Vista's. Because from what I observed, I realized that Vista consumes much more power and thus shortens battery life than XP. So, what I am interested to know is whether running Ubuntu improve battery life significantly or only slightly as compared to Vista.

i depends u see
if u use compiz(the 3d thing) then more power will be used
u can also control the clock speed if it is supported for ur hardware
    get the mouse to the top pannel then right click and click the 'Add to Pannel' scroll to 'system and hardware' there u will see 'CPU frequency scalling'
    by configuring it u can control the speed of ur processor so u can save power

My personal openion is that yes ubuntu does consume less power because it is light weight than even XP in general