This concept design, dubbed the Hungry Battery, is a pretty standard-looking set of batteries when they're all charged up. But unlike normal batteries, which let you know that they're dead by no longer working, these guys actually get thinner as they lose juice.
It's a neat idea. It would certainly be helpful to have a visual indicator of how much power is left. But the way batteries fit into devices makes this seem like it wouldn't really work. If they need to fit in tightly when charged, would thinning down make them loose? If so, these won't work at all. Maybe a visual gauge on the side would make more sense.
Via Yanko Design