I just received a new PowerBook (my first Apple), did a full charge and am now using it with the batter. I changed from "Normal" to "Better Battery Life" and when I did so the screen went all weird. It got better after a little bit and then when I changed it back to "Normal" it did the same. Is this normal? I get all sorts of lines all over my screen and can hardly make out anything. It kind of scares me.