What happens to millions of these? As concern mounts over the impacts of climate change, many experts are calling for greater use of electricity as a substitute for fossil fuels. Powered by advancements in battery technology, the number of plug-in hybrid and electric vehicles on U.S. roads is increasing. And utilities are generating a growing share of their power from renewable fuels, supported by large-scale battery storage systems. These trends, coupled with a growing volume of battery-powered phones, watches, laptops, wearable devices and other consumer technologies, leave us wondering: What will happen to all these batteries once they wear out? Despite overwhelming enthusiasm for cheaper, more powerful and energy-dense batteries, manufacturers have paid comparatively little attention to making these essential devices more sustainable. In the U.S. only about 5% of lithium-ion batteries—the technology of choice for electric vehicles and many high-tech products – are actually recycled. As sales of electric vehicles and tech gadgets continue to grow, it is unclear who should handle hazardous battery waste or how to do it.