battery is fully charged but drains in about 40 minutes

So I have one of the new 13" MacBooks & for some reason my battery is fully charged but drains in about 40 minutes. I usually leave my brightness at like 2 & the backlit keyboard is usually never lit up. My battery has always lasted like 5-6 hours before needing a recharge & all of a sudden it will only last 40 minutes?! Any thoughts, ideas? Thanks for the help guys!

Sounds like maybe your battery went south.... If the machine is still under warranty, make an appointment with an Apple genius to have them check it out. If the battery is defective (or the charging circuitry) they'll repair or replace it at no charge.

You might want to try this first before you take it in.

Regards.