Another key feature the Blue Drive system is its battery technology. Hyundai claims to be the only automaker utilizing lithium-polymer batteries in a production vehicle, the advantages of which are many. According to Hyundai, lithium-polymer batteries offer the same benefits of lithium-ion batteries, but are more robust, lighter, easier to cool, and more easily packaged due to a significantly thinner profile. The automaker further claims that compared to nickel-metal hydride batteries, lithium-polymer batteries are more resistant to changes in temperature, have a slower self-discharge rate, and offer 10 percent greater efficiency with a 40 percent reduction in volume.
Other power-saving tricks have been employed to keep the Sonata Hybrid as efficient as possible. Its Theta II gasoline engine operates on an Atkinson Cycle, making changes to compression and power strokes when the electric motor is operating in unison, conserving energy and boosting fuel economy. Hyundai's Hybrid Power Control management software also features a start/stop system that shuts down the gasoline engine when the vehicle is stationary, automatically restarting it when pressure is reapplied to the throttle.
To help ensure that the Sonata Hybrid is being driven as efficiently as possible, a Hybrid Technology Display is located inside (either on the instrument panel or on the optional navigation display), monitoring which mode the vehicle is being driven in, energy flow inside the vehicle, engine and motor movement, fuel level, battery power level and charge status, and both average and instant mpg.
Much like the gasoline-powered Sonata, Hyundai claims its Sonata Hybrid is a segment leader in many regards, with the lowest curb weight (3457 pounds), most horsepower, and greatest passenger volume (104 cubic feet) of any of its competition from Ford, Nissan, Toyota and Honda. While actual EPA numbers have yet to be released for the Sonata Hybrid, Hyundai is estimating 37/39 city/highway mpg -- figures that place the Sonata right around the top of the pack with Ford's 41/36 mpg Fusion Hybrid. Whether the EPA backs up those figures remains to be seen. Also remaining to be seen is whether cold hard numbers can equate to an all-around better hybrid midsize sedan. For the answer to that question, you'll have to stay tuned.