Is My iPod Battery Dying Too Quick?

I have the 30GB iPod video and lately I've been using it to watch the 3rd season of Lost. One episode usually runs about 44-46 minutes as there are no commercials. I can only get thru about 2 episodes before the battery is fully depleted. Is this normal? I know that watching videos draws much more power then music but shouldn't it last longer then that? My girlfriend has the 180GB iPod with video and it seems to last a lot longer. I was able to watch 4 episodes on it and it still had more then half it's battery life.