Same here. I lowered it to 10 a few weeks ago when I read a post about the heat generation of having your screen on 100 and how the screen can separate. On 10, it is bright enough when even outside. As for battery life, it seems my Storm has a life of its own at times. Sometimes I can get 2 days out of it, then with the same amount of usage I will get maybe 12+.
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I've had mine set at 50, and been thinking about cutting it back. My battery is all over the place depending if I'm watching vids, using BB Maps, or just surfing. So, I don't know how much the backlight matters in extending your life.