Mercedes-Benz's range-topping S-Class now has a "3 liters per 100 km" car. Hot on the heels of the all-electric SLS AMG supercar, the S 500 Plug-In Hybrid packs an electric motor powered by an externally charged lithium-ion battery. The plug-in combines up to 19 miles (30 km) of emissions-free commuting with the acceleration and performance expected of an S-Class.

The S 500 Plug-In Hybrid joins the S 400 Hybrid and S 300 BlueTec Hybrid in the S-Class hybrid line. Unlike those two models, the new S 500 plug-in packs a more powerful hybrid system that offers the option of external charging via a socket on the right side of the rear bumper. Its new high-voltage lithium-ion battery has 10 times the power content of the batteries in the S 400 and 300 hybrids, according to Mercedes.

The S 500 Plug-In Hybrid rumbles to life with the combination of a 328-hp 3.0-liter turbocharged V6 engine and 107-hp (80-kW) electric motor. That translates into a large luxury sedan that brings home impressive 3 L/100 km (78.4 mpg US) and 69 g/km of CO2 emissions. It loses a touch of performance over the non-hybrid S-Class, but with a 5.5-second 0-62 mph (100 km/h) time, it hardly misses a beat.

Four driving modes allow the driver to select the optimal combination of power and efficiency for the conditions at hand. At the most fuel-frugal end of the spectrum, "E-Mode" offers pure-electric driving for up to 19 miles (30 km). On the other end, "E-Save" reserves the fully charged battery for pure-electric driving at a later time. In between, hybrid mode blends electric motor and V6 output. "Charge" mode can be selected to charge the battery from drive components, such as the second-generation recuperative braking system.

The S 500 plug-in also uses what Mercedes terms an "anticipatory Intelligent HYBRID energy management system," which uses navigation information from Mercedes' COMAND Online infotainment system to optimize the output of the hybrid system based upon the conditions (hills, curves and speed limits) expected over the next 5 miles (8 km). The idea is to optimize power usage and charging, such as using battery power before a decline so that the battery power can be restocked during coasting. Mercedes says that the haptic accelerator pedal assists in power monitoring, using resistance to give feedback about the activation of the combustion engine.

Mercedes plans to launch the S 500 Plug-In Hybrid in 2014 and will premiere the model at the Frankfurt Motor Show in September. We'll bring you more information and photos of it from the show floor.

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