What's holding energy tech back? In a Feb. 4, 1957, photo, W.E. Kelley, left, and Robert C. Miller exhibit the nuclear battery, in center of ring at left, powering a radio transmitter. The tiny atomic battery, whose basic material is a radioactive waste byproduct of nuclear reactors, promethium 147, was put on display in New York for the first time. It?s been nearly a quarter of a century since the last big jump in battery technology. As 21st century technology strains to be ever faster, cleaner and cheaper, the battery, an invention from more than 200 years ago keeps holding it back. Credit: AP Photo, file