Whether gliding around city streets or cruising out on the open road, the S 500 Plug-in Hybrid is a superbly serene and relaxing way to travel.
Its hi-tech driveline operates with Swiss watch-like precision and whisper quiet properties in all modes. The transition between pure electric running and the engagement of the petrol engine as it switches into hybrid state is virtually imperceptible.
The combination of petrol power and electric propulsion also provide the plush leather lined saloon with a broad and entertaining range of performance qualities. In electric mode it provides pleasingly urgent step off and flexible properties at speeds up to a limited 87mph.
There are also sufficient reserves on offer in petrol-electric hybrid mode to haul it along with an impressive turn of pace and compelling high speed vigor when the conditions permit.
Despite the weight burden brought on the large battery and all its various ancillaries, Mercedes-Benz says the S 500 Plug-in Hybrid is capable of accelerating from 0 to 62mph in 5.2sec and reaching a top speed limited to 155mph. By comparison, the 45kg lighter Porsche Panamera S E-Hybrid offers respective figures of 5.5sec and 167mph.
Official combined cycle economy is put at 101mpg – a figure that corresponds to average CO2 emissions of just 65g/km.
Mercedes-Benz is realistic enough to acknowledge few motorists, if anyone, will be able to replicate this in everyday driving conditions. Although with a fully charged battery and resolutely light throttle loads you can manage to extract some amazing economy figures out of it, even over extended distances.
I got close to the prescribed consumption figure over an average of 88mpg over a 48-mile route, although 14 miles of it was achieved on electric power alone and it was all at a fairly moderate speed over relatively flat terrain. For the record, the Porsche Panamera S E-Hybrid is claimed to deliver 91.1mpg and 71g/km.
It may offer a bewildering choice of driving modes but it is not a difficult car to operate. You can jump in and drive off as in any of Mercedes-Benz’s more traditional petrol or diesel flagship saloon models without giving it so much as a second thought. But to really get the best out of the S 500 Plug-in Hybrid you need to become familiar with its four main driving modes – a process which takes time and persistence.
Hybrid combines the petrol engine and electric. E-mode offers pure electric running until the battery charge is depleted. E-save allows you to preserve the energy within the battery by favouring the petrol engine until another mode is chosen and allowing the stored energy to be used for pure electric running later on, when entering the London congestion charge zone, for example. Charge employs the petrol engine to top up the battery on the run.
At one point during our first drive of the S 500 Plug-in Hybrid its digital instrument display indicated the battery charge had dipped to just 25 per cent, suggesting its electric range was limited to around five miles. But when I placed it into Charge mode, the energy store was replenished to 85 per cent within 25 minutes, giving it almost 18 miles of electric range.
Happily, the added weight hasn’t affected the ride. Riding on standard 18-inch wheels shod with low rolling resistance tyres – 245/50 at the front and the 275/45 at the rear – the new Mercedes-Benz provides the same cosseting qualities as other S-class models.
A neat feature is the so-called Haptic Accelerator. It operates in combination with the stereo camera mounted within the windscreen, providing an impulse within the throttle to signal you are too close to the car ahead and can recuperate energy by lifting off – at which the S-class automatically switches into a freewheeling state with the petrol engine and electric motor disengaged from the gearbox.
As we noted on the earlier S 300 BlueTEC Hybrid and S 400 Hybrid, the action of the brake pedal is compromised by the need to recuperate energy during braking, lacking for uniform firmness throughout its travel.
Unlike the battery of S 300 BlueTEC and S 400 Hybrid which resided underneath the bonnet, the battery used by the S 500 Plug-in Hybrid is mounted within the forward section of the boot. This robs 95 litres of luggage capacity, reducing it to a total of 395 litres.