Unlike earlier aluminum batteries, which generally failed after only about 100 recharge cycles, Stanford's prototype can cycle more than 7,500 times without any capacity loss -- 7.5 times longer than your average li-ion. The aluminum-ion cell isn't perfect (yet) as it can only produce about 2 volts, far less than the 3.6V that lithium-ion an muster. Plus aluminum cells only carry 40 watts of electricity per kilogram compared to lithium's 100 to 206 W/kg power density. "Improving the cathode material could eventually increase the voltage and energy density," said Dai. "Otherwise, our battery has everything else you'd dream that a battery should have: inexpensive electrodes, good safety, high-speed charging, flexibility and long cycle life. I see this as a new battery in its early days. It's quite exciting."