In March this year, Mercedes-Benz revealed pre-production versions of its new E-Class and C-Class diesel plug-in hybrid models at the Geneva Motor Show. Now, we’re being provided a lot more information about the C-Class variant, which is called the C 300 de. Deliveries of the first units of the C 300 de is scheduled to start in mid-2019. The company will also reveal a plug-in-hybrid version with a petrol engine based on the current C-Class, which will be the replacement for the C 350 e.

The plug-in hybrid operates much like many others do, except that fuel used here is diesel. Under the bonnet, there’s the brand’s OM654 2.0 litre four-cylinder turbodiesel that makes 194 PS (191 hp)/400 Nm and a nine-speed 9G-Tronic automatic transmission.

The electrification aspect sees a 122 PS (121 hp/90 kW)/440 Nm electric motor being integrated together with the transmission’s torque converter and clutch into a single unit. This is to allow for a more compact design, and the finished item is just 108 mm longer than a standard non-hybrid 9G-Tronic unit.

This design differs from the company’s second-gen system, whereby the electric motor was connected directly with the transmission input and a wet start-off clutch was used as a starting and separating clutch. A torque converter between the electric motor and the transmission handles vehicle set off, and the separating clutch can be redesigned to reduce losses.

Meanwhile, the electric motor draws power from 13.5 kWh lithium-ion battery, which is a major step up from the 6.38 kWh unit found in the C 350 e. The company revealed that this is possible thanks to an increase in cell capacity from 22 to 37 Ah following the switch in cell chemistry from lithium-iron-phosphate (LiFePo) to lithium-nickel-manganese-cobalt (Li-NMC).

The battery can be charged via the car’s regenerative braking system while driving, or by plugging the car into a power outlet. To allow for faster charging, Mercedes-Benz has fitted a new water-cooled on-board charger on the C 300 de that boasts a charging capacity of 7.4 kW – double that of the C 350 e (3.7 kW).

With the brand’s latest 22kW Wallbox (Type 2 connector), the battery can be charged from 10 to 100% state of charge in about 1.5 hours. That is 15 minutes less than the time it takes a C 350 e to recharge its 6.38 kWh battery using the previous 3.7 Wallbox, despite the C 300 de having a larger battery capacity. You can also plug the car to a conventional domestic power socket, whereby recharging takes around five hours.

Mercedes-Benz says the total system output is rated at 306 PS (302 hp) and torque is limited to 700 Nm, the latter available from just 1,400 rpm. Performance-wise, you’re looking at a 0-100 km/h time of 5.6 seconds (5.7 seconds for the Estate), and a top speed of 250 km/h. The plug-in hybrid has a claimed fuel consumption of as low as 1.4 l/100 km (1.5 l/100 km for the Estate), with combined CO2 emissions from 38 g/km, following the NEDC method of testing.

Four operating modes for the powertrain are available here, including Hybrid, which is the default setting; E-Mode that allows for all-electric driving; E-Save to reverse the charged battery until needed; and Charge that charges the battery while driving. In E-Mode, a range of 57 km is touted along with a top speed just over 130 km/h.

Drivers will also have access to the ECO Assist system that factors in route profiles, speed limits and distance from vehicles ahead to generate driving recommendations and efficiency strategies. For instance, the driver is prompted when appropriate to come off the accelerator like when a speed limit is approaching. Data from the car’s navigation system, camera and radar sensors are also considered to adjust the specific speed/route profile.