A novel fuel-cell power source runs on everything from soft drinks to tree sap and could go 4 × longer between "charges" than conventional lithium-ion batteries, say researchers at St. Louis University in Missouri.

Enzymes in the device convert fuel — in this case, sugar — into electricity, leaving behind mostly water. Researchers have run it on glucose, flat sodas (carbonated beverages don't work as well), sweetened drink mixes, and tree sap. So far, ordinary table sugar (sucrose) dissolved in water has proven to be the best fuel.

Sugar fuel cells could eventually replace lithium-ion batteries in many portable electronics devices. A postage-stamp-sized prototype has ample power to run a handheld calculator, for example. A larger version could charge portable electronic equipment on the battlefield. Portable cell-phone rechargers may be the first application for the technology. Such rechargers could use replaceable cartridges filled with sugar solution. Stand-alone units are the ultimate goal, says the group, though don't expect to see commercial sugar fuel cells for three to five years.