About Benz S400

In stark contrast to such luxury hybrids as the Lexus LS600hL and the new BMW 7-series hybrid—both of which, perplexingly, make more power than their less-green luxocruiser counterparts—Mercedes’ first hybrid, the S400, is surprisingly rational. Not only does it downsize from the S550’s 382-hp V-8 to a combined output of 295 horsepower (supplied by the corporate 3.5-liter V-6 and an electric motor), it also costs less. Whereas the Lexus and BMW hybrids come at a premium of tens of thousands of dollars, the S400 is the cheapest S-class, by $3650, starting at $88,825 (before an $1150 federal tax credit). Transforming the S-class into a mild hybrid—it cannot run on electric power alone—is the addition of a roughly 65-pound, shoebox-size, 0.9-kilowatt-hour lithium-ion battery pack under the hood and a 50-pound electric motor sandwiched between the engine and a seven-speed automatic. Despite the additional weight of the hybrid gear, however, the S400, at 4594 pounds, is the lightest ninth-generation S-class we’ve tested.