The Mercedes-Benz S-Class has long been an automotive icon, one of the best cars in the world--and for more than 50 years, the vehicle of choice for prosperous German businessmen.

Against it, the BMW 7-Series and the Audi A8 still seem like pretenders. In Manhattan or Tokyo or Rio or Dubai, the presence of a black S-Class idling at the curb says more than either of those other cars can.

The all-new 2014 Mercedes S550 launched last fall, and the company's first-ever plug-in hybrid S-Class has just gone on sale in Europe, awkwardly labeled S500 Plug-In Hybrid.

2016 Mercedes-Benz S550 Plug-In Hybrid, U.S. pre-production car tested, Stuttgart, Germany, Aug 2014

2016 Mercedes-Benz S550 Plug-In Hybrid, U.S. pre-production car tested, Stuttgart, Germany, Aug 2014

It will land in North America next spring, as a 2016 model, and now we've driven a prototype of that car. (In North America it will use the familiar S550 number with "e" and "Plug-In Hybrid" appendages.)

ALSO SEE: 2014 Mercedes-Benz S550: First Drive (July 2013)

During a day's drive of well over 100 miles on the highways, arterial roads, and even country lanes in and around the company's headquarters city of Stuttgart, the plug-in S550 did everything that was asked of it--and, importantly, did it in the manner you would expect of an S-Class.

It's significant that Daimler chose to launch the new plug-in hybrid powertrain in its most prestigious and significant volume car. It signals a certain confidence that the system will meet the expectations of S-Class drivers and passengers.

In large part, it does.

2016 Mercedes-Benz S550 Plug-In Hybrid, U.S. pre-production car tested, Stuttgart, Germany, Aug 2014

2016 Mercedes-Benz S550 Plug-In Hybrid, U.S. pre-production car tested, Stuttgart, Germany, Aug 2014

The basic powertrain is a 3.5-liter V-6 engine with a single electric motor producing 85 kilowatts (114 horsepower) of peak power sandwiched between the engine and an adapted version of Mercedes' own seven-speed automatic transmission.

Total output of the combined powertrain is 325 kW (436 hp), and Mercedes-Benz quotes a 0-to-62-mph acceleration time of 5.2 seconds. The motor is powered by a trunk-mounted 8.7-kilowatt-hour lithium-ion battery pack (of which 6.4 kWh is usable).

It's a more powerful version of a powertrain that was shown way back in 2009, when the company first revealed a concept car that suggested the startling notion of offering a hybrid S-Class with a plug.

For a combination of regulatory reasons, plus the anticipation imposition of zero-emission zones in some old European city centers, plug-in hybrids are starting to supplant conventional hybrids from German makers--at which they have made only half-heated attempts in any case.

2016 Mercedes-Benz S550 Plug-In Hybrid, U.S. pre-production car tested, Stuttgart, Germany, Aug 2014

2016 Mercedes-Benz S550 Plug-In Hybrid, U.S. pre-production car tested, Stuttgart, Germany, Aug 2014

The plug-in hybrid S550 is the first from Mercedes, but it signals an upcoming revolution in which every model--up to 10 separate volume cars, Daimler told us--will offer such a powertrain by 2020.

Following the S550 in Spring 2015 will be both a C-Class version and an updated ML-Class roughly a year from now.

MORE: Three Mercedes Plug-In Hybrids On Sale By End Of 2015: S-Class, C-Class, ML-Class:

And Daimler isn't the only one. The Porsche Panamera S E-Hybrid replaced last year's Panamera S Hybrid--and it now makes up 14 percent of U.S. Panamera sales and 9 percent globally.

2016 Mercedes-Benz S550 Plug-In Hybrid, U.S. pre-production car tested, Stuttgart, Germany, Aug 2014

2016 Mercedes-Benz S550 Plug-In Hybrid, U.S. pre-production car tested, Stuttgart, Germany, Aug 2014

That Panamera model may be the closest direct competitor to the S-Class Plug-In Hybrid, and both cars share certain similarities.

They can accelerate away from a stop solely on electric power--if not at full throttle, certainly at a respectable pace that doesn't require the driver to treat the throttle like a fragile eggshell.

When maximum acceleration is required, the engine switches on after the driver pushes through a slight resistance to get what the company called "kickdown" mode.

Acceleration accomplished, though, the S550 plug-in can cruise at speeds of 60 mph in all-electric mode when conditions permit.

And its transition between power modes is particularly good--all but undetectable without watching the power meter/tachometer.

2016 Mercedes-Benz S550 Plug-In Hybrid, U.S. pre-production car tested, Stuttgart, Germany, Aug 2014

2016 Mercedes-Benz S550 Plug-In Hybrid, U.S. pre-production car tested, Stuttgart, Germany, Aug 2014

Mercedes offers four power modes, of which the most aggressive is the Sport setting. Driven aggressively, this allows the big sedan to hustle along aggressively--but keeps the engine on the whole time, using the electric motor to provide boost, almost like an instantly-on turbocharger.

The default setting is E, which operates the car under electric-only mode when possible, then switches over to conventional hybrid operation when the battery is depleted.

The ultra-efficient E+ mode isn't as annoying in the S-Class--thankfully--as is less expensive hybrids, and while it's notably slower, it doesn't kill ventilation altogether or make the car so slow that it holds up traffic.

Finally, there's also the E-Save mode, which keeps battery charge at a steady state for later use, and runs the car as a hybrid from the start.

2016 Mercedes-Benz S550 Plug-In Hybrid, U.S. pre-production car tested, Stuttgart, Germany, Aug 2014

2016 Mercedes-Benz S550 Plug-In Hybrid, U.S. pre-production car tested, Stuttgart, Germany, Aug 2014

Overall, the virtues of the S-Class have been maintained despite the unusual and complex powertrain--with the added fillip that plugging the car in gives you perhaps 15 miles of range on a full charged battery, during which you may well not use the engine at all.

DON'T MISS: Mercedes-Benz C350 Plug-In Hybrid Powertrain Specs Revealed

To quote from our First Drive on the brand-new gasoline S550 a year ago:

You'd have to be a true cynic to find fault with the Mercedes-Benz S Class' passenger comforts. The 2014 S550 has spacious accommodations, superb front seats, easy access for those in back, and a fillip of first-class accoutrements to go with occasionally fiddly ergonomics. There's a bit more room inside than before--all U.S. cars are a longer-wheelbase variety--and every cubic inch is filled with systems to nurture passengers.

2016 Mercedes-Benz S550 Plug-In Hybrid, U.S. pre-production car tested, Stuttgart, Germany, Aug 2014

2016 Mercedes-Benz S550 Plug-In Hybrid, U.S. pre-production car tested, Stuttgart, Germany, Aug 2014

That's as good a summary as any. You might say that the company now offers the S-Class of plug-in hybrids.

Based on a day's driving, that bodes well for its future electrified vehicles.

Our only question will be whether the owners of $100,000-plus luxury sedans will plug them in as faithfully as owners of lesser plug-in electric cars.

For that, we'll have to wait for real-world usage.

The 2016 Mercedes-Benz S550 Plug-In Hybrid goes on sale next spring, with pricing, trim packages, and options to be released closer to that date.