Macbook pro (Early 2011) battery.

I just got my 15 inch quad core macbook pro in the mail. I quickly calibrated the battery and fully charged it. It is advertised to get 7 hours when browsing the internet and it simply doesnt. When i am not touching my computer the battery says 8 hours, and i'm like ok thats awesome. So as soon as i load up any wed site, even a non flash no video website, the battery quickly drops to 4 to 3, and sometimes even two hours. I was wondering if this is normal because it sure doesn't sound normal. Thanks.