First Tests

2015 Mercedes-Benz S550e PHEV First Test Review

High-Rolling Hybrid Is No Less an S-Class

High-Rolling Hybrid Is No Less an S-Class

If you have the means to buy a Mercedes S-Class, chances are you don’t need to worry too much about fuel economy. But for those who want ultimate luxury without the gas-hog image that comes with it, there’s the S550e plug-in hybrid. With a larger battery pack, a more powerful electric motor, and a new twin-turbo V-6, the S550e surpasses its predecessor, the S400 Hybrid, in every way.

Like the S400 Hybrid, the new model uses a lithium-ion battery pack. But a larger capacity of 8.7 kW-hrs and a beefier electric motor grant it the ability to run on electric power alone. The twin-turbo, 3.0-liter V-6, which has been rolled out in several other Mercedes-Benz models, is good for 329 hp and 354 lb-ft of torque by itself. The V-6 combined with the 114-hp, 251-lb-ft electric motor produces a total system output of 436 hp and 479 lb-ft. That’s down from the non-hybrid S550, which is powered by a twin-turbo, 4.7-liter V-8 that makes 455 hp and 516 lb-ft. You’ll feel the difference, but power never feels inadequate (at least in Hybrid mode).

The S-Class plug-in has four operating modes, including Hybrid, E-mode, Charge, and E-save. In Hybrid, the electric motor supplements the gas engine by providing boost when accelerating and taking over at cruising speed as long as the battery has sufficient charge. E-Mode relies solely on the electric motor, with the gas engine only available if you pass the threshold of the haptic accelerator pedal. Doing so requires no small amount of pressure. You have to really step on it to get the V-6 to switch on. Acceleration at full “throttle” in E-mode is fine until about 30 mph. After that, the electric motor seems to run out of steam, and it’s a slow climb up to highway speed. But once you’re at speed, driving in E-mode feels normal again, and there’s a distinct feeling of satisfaction at seeing the tachometer at 0 rpm.

Testing revealed that the S-Class plug-in is slower than the less eco-friendly model with the twin-turbo V-8, but not by that much. The S550e accelerated from 0 to 60 mph in 5.0 seconds flat to 4.7 seconds for a rear-drive 2014 S550 we tested previously. The quarter mile for the plug-in came in 13.6 seconds at 104.9 mph, or 0.4 second slower than the standard S550, which completed the same distance in 13.2 seconds at 107.7 mph. Because of the hybrid system’s extra 460 pounds, the S550e needs more room to stop, requiring 123 feet to come to a halt from 60 mph versus 119 for the non-hybrid S-Class. Both cars posted identical figure-eight times, but testing director Kim Reynolds noted that the hybrid’s stability control system wouldn’t let it hustle through the turns. But then again, why would an S-Class driver want to wring out this full-size luxury sedan? They might spill the boss’ Dom Pérignon.

Driving the S550e is everything you’d expect from an S-Class. It offers one of the smoothest rides in the business, and it’s quiet, too. Noise from the engine and outside is already pretty muted in a regular S-Class, but when running the S550e on all-electric power, the cabin becomes eerily silent. The constant turning on and shutting off of the engine doesn’t disturb that peace too much, either. You get a subtle vibration, but unless you’re watching the tachometer, you won’t know it’s the engine switching on. Brake feel is just as refined. Unlike other cars where it’s easy to tell when the regenerative brakes switch to the traditional hydraulic stoppers, the S550e is practically seamless in its braking operation. When I first got in, I braced myself for the jerkiness that normally comes with learning a hybrid’s brakes but was surprised to find a very linear, very normal-feeling brake pedal.

During my drive, I plugged the S550e in four times, all at public Level 2 chargers. Mercedes estimates that a full charge takes 2 hours and 45 minutes on a Level 2. That sounds about right based on my experience. I plugged in at an outlet mall for a little more than an hour and got to 25 percent at a cost of $2.08 USD. That netted a whole 5 miles of indicated electric range. That’s not a great value considering how cheap gas is right now, but not all chargers will be as expensive. And with the S550e being a hybrid, you don’t even really need to charge in public. If the charger is free or gets you a primo parking spot, then by all means fill ‘er up. Otherwise, it’s probably best to just charge at home during off-peak hours when electricity is cheapest. In the future, the S550e could feature wireless charging.

Mercedes says the S-Class plug-in has an all-electric range of around 20 miles. You can milk that, though, if you have a nice, long downhill section such as the Grapevine just outside of L.A. By coasting through most of the Tejon Pass, I was able to charge the relatively small battery pack quickly. When the road became flat again, I had a full charge to carry me 20 emission-free miles. But you can charge the car while driving even if you don’t have a mountain road to coast down. Charge mode uses the gas engine to juice up the battery as you drive. It takes a while to get to 100 percent, but it works. However, since you’re not benefitting from the electric motor’s assistance that entire time you’re charging, any gas savings netted in E-Mode are probably a wash. Still, it’s nice to have options.

That’s kind of what the S550e is all about. You can plug in if you want to run on pure battery power (for a brief time), or you can skip the charger and just drive it as a regular hybrid. Either way is fine, and neither option detracts from the S-Class experience. The 2015 S550e starts at $95,325 USD, but because our tester came loaded with a number of different packages, the as-tested price soared to $114,315 USD. For the 2016 model year, the standard S550 and the S550 plug-in will have the same starting price of $96,575 USD. Considering the difference in EPA fuel economy ratings, you might think picking the hybrid is a no-brainer, especially since it takes only a minor hit to performance. But our own Real MPG results suggest the gap isn’t actually that big. In our tests, a standard 2014 S550 performed better than its EPA numbers, posting a score of 18.8/27.8 mpg (12.5/8.5 L/100km) city/highway. The S550e, on the other hand, earned a Real MPG score of 22.8/27.2 mpg (10.3/8.5 L/100km), which is lower than its EPA rating of 24/30 mpg (9.8/7.8 L/100km). It’s also worth noting that the S550e will only be available in the 10 states that follow California’s Zero Emission Vehicle standards.

If it were my money, I’d choose the model with the undiluted twin-turbo V-8. Because hey, I’m rich in this scenario. But if I had a short commute, drove mostly in city traffic, and had green-leaning friends to impress, the S550e would be an enticing proposition. Whichever one you choose, at the end of the day you’ll have a Mercedes-Benz badge and a model designation that begins with S. And that’s always a winning combination.

2015 Mercedes-Benz S550e
BASE PRICE $95,325
PRICE AS TESTED $114,315
VEHICLE LAYOUT Front-engine, RWD, 5-pass, 4-door sedan
ENGINE 3.0L/329-hp/354-lb-ft twin-turbo DOHC 24-valve V-6 plus 114-hp/251-lb-ft DC electric motor; 436 hp/479 lb-ft comb
TRANSMISSION 7-speed automatic
CURB WEIGHT (F/R DIST) 5,250 lb (47/53%)
WHEELBASE 124.6 in
LENGTH x WIDTH x HEIGHT 206.5 x 74.8 x 58.7 in
0-60 MPH 5.0 sec
QUARTER MILE 13.6 sec @ 104.9 mph
BRAKING, 60-0 MPH 123 ft
LATERAL ACCELERATION 0.81 g (avg)
MT FIGURE EIGHT 26.5 sec @ 0.70 g (avg)
EPA CITY/HWY/COMB FUEL ECON 24/30/26 mpg*
ENERGY CONS., CITY/HWY 140/112 kW-hrs/100 miles*
CO2 EMISSIONS, COMB 0.74 lb/mile*
EPA RANGE 14 miles
*Charge-sustaining operation