I always use my laptop with direct power and I use it with battery only during load-shedding (for few minutes) or when I have some emergency work.
But I read an article "Keeping Your Laptop Plugged in All the Time Will Kill Its Battery Faster". It says when the battery hits 100% you should unplug it and use it on battery. This will keep the cells in lithium battery active and will make the battery life up to 4 times longer.
If I use it on battery I don't get the full brightness / contrast, I mean overall look of the screen becomes very dull, but with direct power it is great.
How do you use your laptop? Don't you see the dull brightness / colors?
Article link: http://www.wired.com/gadgetlab/2013/09/laptop-battery/