Dark Silicon and Smartphone Batteries

I have had discussions with several friends lately about the increasing complexity of smartphones and the contribution of that to short battery life. So I bit at an article in CACM, about dark silicon. Had to admit I had no idea what dark silicon was. The article says: " ... A new smartphone chip prototype under development at the University of California, San Diego will improve smartphone efficiency by making use of "dark silicon"—the underused transistors in modern microprocessors. UC San Diego computer scientists presented GreenDroid, the new smartphone chip prototype at the recent HotChips symposium in Palo Alto, CA ... "