My Asus VIvo Tab RT batterry drains 5% ever 15 minutes

I just got my Asus Vivo Tab RT for $399 from Future Shop, and I knew beforehand that the tablet would have up to 9 hours video-playback battery life.

However, I just have my tablet on Idle and doing some light web browsing, and I learned that my tablet's battery drains 5% every 15 minutes, 20% an hour, 5 hours of battery life from light usage. Is this normal? Or I should be changing some of the settings? I already turned of GPS, NFC, and even use the lowest screen brightness as possible.

I'm kind of dismayed, but hey, I got the Tablet for $399 + free keyboard dock (the keyboard dock hopefully will ship soon).