A New Wrinkle in Hybrids Does Away With Batteries - New York Times

A New Wrinkle in Hybrids Does Away With Batteries: prototype hybrid system using hydraulic fluid and a high-pressure pump instead of electrical current and a generator. In this design, energy is stored in a series of pressurized tanks, rather than in nickel-metal hydride or lithium-ion batteries; the energy moves not as high voltage current in copper wires but as hydraulic fluid pressurized to thousands of pounds per square inch.

What a great idea!