Yes, Brett928S2, we know...answer the question.
First, the bad news - no laptop that can play BF3 on high will last 3-4 hours unplugged gaming. If you are just browsing/typing, you may get that on a monster, but not gaming.
Second, the good news - you can average ~40fps with a 580M according to this:
http
/www.pcper.com/reviews/Graphics-Cards/Mobile-GPU-Comparison-GeForce-GTX-580M-and-Radeon-HD-6990M/Bad-Company-2-Deus (The 6990M may also work, and some laptops have SLI'd 560Ms, which should also handle it at about that level).
Now, which laptop...
Well, the Alienware M17x is $1824 with either the 580M or 6990M -
http
/configure.us.dell.com/dellstore/config.aspx?oc=dkcwvn1&c=us&l=en&s=dhs&cs=19&model_id=alienware-m17x-r3
Sager on the other hand...
Has the NP8170 with the 6990M starting at $1594:
http
/www.sagernotebook.com/index.php?page=product_customed&model_name=NP8170
Or the 18" NP8180 for $1799 with SLI'd 560Ms...
http

/www.sagernotebook.com/index.php?page=product_customed&model_name=NP8180