Modern batteries aren't hampered so much by their capacity as their long-term lifespan -- a lithium-ion pack can easily become useless after a few years of heavy use. That's bad enough for your phone, but it's worse for energy storage systems that may have to stick around for the long haul. If Harvard researchers have their way, you may not have to worry about replacing power backs quite so often. They've developed a flow battery (that is, a battery that stores energy in liquid solutions) which should last for over a decade. The trick was to modify the molecules in the electrolytes, ferrocene and viologen, so that they're stable, water-soluble and resistant to degradation. When they're dissolved in neutral water, the resulting solution only loses 1 percent of its capacity every 1,000 cycles. It could be several years before you even notice a slight dropoff in performance.