While the Chevrolet Volt gets the headlines, and the Toyota Prius most of the sales, Mercedes-Benz has managed to leapfrog the competition and become the first automaker to put a next generation lithium-ion battery pack into a production hybrid.

Score one for the inventors of the automobile.

New technology aside, the Mercedes-Benz S400 is also the company’s first hybrid of any type to make it into showrooms. For 2010, the entire S-Class lineup has been given a very minor refresh that includes a new grille, headlight clusters with flavor-of-the-day LED running lights, and new front and rear bumpers. The S400 shares in all of those updates and, aside from a couple of hybrid badges outside and in, the land yacht is indistinguishable from its S-Class brethren, unless you look under the hood. Even then, it's tough to tell the difference.

Click here for a SLIDESHOW of the S400

The powertrain in the S400 is comprised of a 3.5 liter V6 engine, a 7-speed automatic transmission, and a small electric motor mounted between them. The hybrid battery itself is no larger than the 12-volt lead-acid type used to start conventional S-Class sedans, and fits into the same space in the engine bay where one of those is normally found.

The hybrid system in the S400 is mild, which means it never operates in electric-only mode the way the one in the Toyota Prius does. Instead, the 20 horsepower electric motor assists the internal combustion engine under acceleration, and allows it to shut off whenever the vehicle comes to a rest and instantly restart when the driver steps on the erstwhile 'gas' pedal. The design trades maximum fuel efficiency for simplicity and lower cost, battery not included.

The primary reason we haven't seen a hybrid with a lithium ion pack before is expense, so it's maybe not a surprise that the first one comes in a car with a price tag of $87,950, excluding a $1,150 green tax credit. Mercedes-Benz is hush hush on how much of that money goes towards the battery, but outside estimates range from $8,000 on up. The automaker is likely keeping the number under wraps in the hope that by the time the government mandated 8-10 year/100,000-150,000 warranty runs out, the replacement cost will be down to more palatable levels.

Until then, the bottom line is that the S400 has an EPA rating of 19 mpg city and 26 mpg highway. No, those aren't headline-grabbing numbers, but they are impressive for a small battleship, and identical to the ones found on the window sticker of Mercedes-Benz's own E350 sedan, which is about 3/4 the size of the S400. Compared to the V8-powered standard bearer of the S-Class line, the S550, the S400 returns 15% percent better combined fuel economy, and 25% more miles in city driving.

Away from the EPA labs, I found that 30 mpg wasn't just attainable, but often unavoidable. The S400 regularly hit that mark, even at highway speeds not normally associated with efficiency. Over the course of 600 miles of mixed driving, the car averaged an even 25 mpg, and I enjoyed every one of them.

I'm still not exactly clear on what constitutes a plutocrat, but I know that I feel like one behind the wheel of an S-Class, even one with somwhat green credentials like the S400. The car is a rolling isolation chamber that wafts you along in a "get out of my way I'm coming through" sort of manner. The hybrid may be down on power compared to the S550, but with 295 hp and 284 lb-ft of torque, it's still about as quick as a Mazda Miata. If that's not satisfactory enough for you, fuel efficiency is probably not a priority of yours anyway.

While it's not quite as nimble as a little roadster, the S400 is very composed, even on roads of the windy, two-lane sort. The air suspension keeps the sedan flat through turns, and flattens out any bumps in the road before they manage to disturb you.

Most impressive is how unobtrusive the hybrid system goes about its business. The engine starts and stops with hardly a shudder, and there’s no variation or funkiness in the power delivery at speed. The regenerative brakes, often the Achilles’ Heel of hybrid systems, feel so normal that you’d never notice a difference if you weren’t looking for it very hard.

The cabin of the 2010 S-Class sees even fewer modifications than the exterior. New ambient lighting and a Napa leather-covered steering wheel pretty much round out the changes. Navigation, lane departure warning, and massaging seats with active bolsters that squeeze you during paparazzi-evading maneuvers are among the usual luxury options available.

Of course, the 900-pound gorilla that would fit nicely in the gargantuan back seat of the S400 is diesel, and why Mercedes-Benz didn't put an engine that burns it into the S-Class instead of the complicated and costly hybrid setup. Call it a hedge. Despite the widening use of the fuel German imports these days - Mercedes-Benz currently has four vehicles with diesel engines in its own lineup - and pump prices on par with gasoline, the U.S. still hasn't gotten over the oil-burning hump the way people in the old countries have. The good news is, we're not missing out on much. European market S350 diesels get 30.5 mpg in fuel economy testing over there, while the S400 is rated at 29 mpg on the same cycle.

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Although it's unlikely that the S400 will overtake the Toyota Prius as the best-selling hybrid in America, there's no reason that it shouldn't be the best-selling S-Class. The price makes it the most-affordable model in the lineup, and for those who buy them to sit in the back seat with that gorilla while being driven from one board meeting to another, performance hardly matters. In any case, the touch of green that comes with it, both in savings and image, should make up for any other inadequacies.


Mercedes-Benz S400 Hybrid

Base Price: $87,950

Type: Front-engine, rear-wheel-drive, 4-door sedan

Powerplant: 3.5L V6 w/electric motor

Power (net): 295 hp, 284 lb-ft torque

Transmission: 7-speed automatic

MPG: 19 city/26 hwy

What do you think of the S400?

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