85 watts not enough?

I recently purchased an early 2011 15" MacBook Pro. I am finding that when I work it hard (mostly using and rendering video from Motion), my battery actually drains while plugged in. Like just now my battery we fully charged 100% and I let Motion render for about 15 minutes and when I came back my MagSafe light was orange and my battery was at 95%. Is it just because my computer is pulling more than 85 watts of power? I did get the 2.3GHz processor which I presume take more power as well as the GPU probably takes a good amount of power as well.

I have had 2 15" MacBook Pro's prior to this one, however they have both been the $1999 model at the time, and were both Core 2 Duo machines which may not pull as much power?

I'm just wanting to know if others are experiencing this or if there is something potentially wrong with my machine.

Thanks!

Matt