on the laptop you can change the battery settings. I know when i set mine to "power saver" my game starts to lag- i would imagine that would have more impact since if you turn down the graphical settings, the computer may just use the extra power to do something else and thus you end up with very little change in battery life.

if you change the battery power setting, however, it limits the amount of battery the computer can use at any one time.

at least, that's my theory. i'm probably wrong