Are you running Windows 7 on a laptop? You may be interested to know that there's a problem with Windows 7 on laptops, where Windows effectively kills your battery. And I don't mean, "my battery just got drained to 0%, time to recharge." Instead, Windows 7 may permanently damage (2) (3) (4)your laptop battery. Even if you roll back to Windows XP - which many people have done.
Microsoft Technet has a forum thread on this topic, where users report problems with many different brands of laptops. The thread dates back to June 5 2009 - when Windows 7 was still in "Beta" - and continues to be updated with more comments. That's at least 8 months, and no fix yet from Microsoft! (Sound familiar?)
Microsoft is convinced the problem relates to a BIOS problem, but several comments in the forum suggest not.
I hope you bought a spare laptop battery.