Our goal on the German autobahn is usually to peg a brag-worthy top speed. This time? We’re cruising along at a gentle 60 mph, enjoying gas-free transportation—and a free massage—courtesy of the 2015 Mercedes-Benz S550 Plug-in Hybrid.

Not another marketing exercise.

Although there are more exciting limits we could be exploring on the autobahn than how fast we can drive in pure-electric mode, few are more important. Premium hybrids, once glorified marketing exercises, are becoming essential. The ramp up of strict C02 caps in Europe, China, and the United States has luxury brands, particularly the European ones, scrambling to increase fleet-wide fuel economy. The 2015 Mercedes-Benz S550 hybrid you see here “forms the spearhead of a plug-in hybrid offensive from Mercedes-Benz,” says R&D chief Thomas Weber. Between now and 2017, the automaker will roll out ten plug-ins.

The S-class pairs Mercedes’ familiar 3.0-liter twin-turbo V-6 with a 114-hp electric motor and an 8.7-kwh lithium-ion battery pack. As the first part of its name implies, it will be positioned alongside the S550 V-8 and will come with similar features and options, although the hybrid will only be available with rear-wheel drive. The “plug in” modifier makes clear that this is a much more capable hybrid than what Mercedes offered on the last-generation S-class. It can travel on battery power for up to 20 miles, and it will recharge in about 2 hours from a 400-volt charger (or 2 hours 45 minutes with a 230-volt charger). What we don’t yet know is what EPA fuel economy numbers it will receive, given the peculiarities and politics of rating plug-in hybrids.

Keep it cool and quiet

The first thing you notice looking at the new 2015 Mercedes-Benz S550 Plug-in Hybrid (called S500 in Europe) is how little you notice. No decals, no special grille, no special colors. Only small, “plug in hybrid” lettering on the trunk in Mercedes’ typical sans-serif font hints at the new powertrain. Mercedes says even this identification is included mainly so roadside responders know they’re dealing with batteries. “We always think of Mercedes-Benz as our brand,” says S550 product manager Matthias Kuchenbecker.

The identity becomes clearer when the trunk lid opens, revealing the lithium-ion battery pack. This junk in the trunk takes up 3.4 cubic-feet of cargo space and prevents a pass-through from the back seat. A plus side of having batteries on board is that the S550 hybrid can cool the interior to a preset temperature and/or preheat your seats, steering wheel, and arm rests.

Otherwise, this is just your run-of-the-mill, $95,000+ S-class cabin, replete with massaging chairs, a digital instrument panel, and an automatic perfume spritzer. The Comand rotary controller works the same as always, perhaps too much so, as rivals BMW and Audi have both leaped ahead with better integrated and easier-to-operate telematics.

Whispering through the cities, roaring on the autobahn

Driving an S-class has always been a serene experience. The plug-in version takes that to a new level. We are whisked through the streets around Daimler headquarters in battery-powered silence. The road, wind, and ambient noises that usually become more noticeable in electric vehicles can’t penetrate this rolling fortress of double-paned glass.

Most hybrids offer multiple driving modes. The 2015 Mercedes-Benz S550 offers that and then some. First there are four settings for battery usage: hybrid; all-electric E-mode; battery-preserving E-save; and E-charge, where the gasoline engine replenishes the battery. When in hybrid mode, one can, via a separate switch, select a setting for the seven-speed automatic—sport, comfort, and E+. No doubt, the German engineers love the ability to fine-tune the powertrain so precisely. It’s a bit much for us. A simple EV/hybrid/performance hierarchy would be much easier for drivers to navigate. On one occasion the powertrain seems confused, as well. With a colleague at the wheel in traffic, the car lugs for several seconds as if we’re stuck in a high gear.

Appropriately for a car that offers pioneering autonomous driving features, the 2015 Mercedes-Benz S550 goes beyond the typical hybrid’s encouragements to drive efficiently. The accelerator pedal actually pushes back at your foot when the S550’s suite of sensors and onboard computers think you could be going a bit easier. Follow its dictates, and you can drive gas-free at speeds as high as 87 mph. You can always override the system by jamming down on the pedal. A kick down switch fires up the 329-hp V-6, even when you’re in EV mode.

After the novelty of driving slow on the autobahn wears off, we switch from electric to hybrid mode and let the wave of torque from the electric motor and the turbo V-6’s power carry us up to the speed of traffic. Because it carries some 450 pounds of extra hardware, the hybrid takes about a half tick longer to accelerate to 62 mph than the V-8-powered S550—5.2 seconds versus 4.8 seconds. That’s still wondrously quick for a car that feels and smells like a moving massage parlor. The standard air suspension doesn’t sweat the extra pounds, providing the same creamy yet planted ride we’ve come to associate with Mercedes. The brakes, with their regenerative functionality, engage a little softly but not offensively so. The biggest sacrifice versus the V-8 car is the sound that accompanies the push in the back. We fault not the electric motor but the rather pedestrian sounding V-6. An inline six would, no doubt, be smoother and more refined. When we ask Weber about the one Mercedes is reportedly developing, he just smiles.

Understated or underwhelming?

The $100,000 question here is whether the elite customers who buy an S-class, people who hardly obsess over their fuel budgets, will bother to buy the Mercedes-Benz S550 Plug-in Hybrid. Weber suggests this is a challenge for the marketing department and dealer network. He also notes, as do many auto executives, that higher gas taxes would go a long way toward ensuring there’s a market for the efficient cars the government is ordering carmakers to build. Both good points, but we also think Mercedes needs to think outside the box to figure how to present green technology in a more exciting and more intuitive way.

Overall, though, the 2015 Mercedes-Benz S550 Plug-in Hybrid impressively electrifies the S-class experience without unduly altering or cheapening it.

2015 Mercedes-Benz S550 Plug-in Hybrid Specifications

On Sale:Summer 2015

Price:$95,500 (est.)

Engine:3.0-liter twin-turbo V-6, electric motor

Power:436 hp (combined)

Torque:479 lb-ft (combined)

Transmission:7-speed automatic

Drive:Rear-wheel

L x W x H:206.5 x 74.8 x 58.8 in

Wheelbase:124.6 in

Curb weight:5093 lb

Fuel Economy:84 MPGe, combined (European testing)

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