Lithium ion batteries are great. They've taken us miles beyond traditional non-rechargeable batteries. But, and you might have heard about this, they sometimes explode. They're also reaching the limit of their capacity per kilogram. One hundred fifty watt-hours per kilogram is a great number for a Li-Ion battery, but in the tech world, everything needs to double every few years, and if we're not going to do it with Li-ion batteries, we need to find something new. Thin film batteries are, of course, currently far to expensive for retail. But if Silicon Valley has taught us anything, it's that a technology in demand never stays expensive for too long. (via http://www.ecogeek.org/)