Much has changed since we .
Having come close to production during the latter half of 2013, only to be cancelled at the final hour due to concerns over its less-than-dazzling range, the first-generation of electic powered supercar has now been extensively re-engineered under the watchful eye of research and development boss Ulrich Hackenberg.
Among the key developments brought to the low-slung two-seater are a new pair of electric motors and a significantly larger battery that is claimed to extend its range by a significant 200km to somewhere in the region of 450km – in the process placing it on par with the .
Like all existing R8 e-tron developmental prototypes on the Audi test fleet right now, the example driven here continues to be based around the first-generation R8.
There are subtle exterior design changes, including active air ducts that open at a predetermined speed, a revised bonnet with an air extractor for improved air flow, a flat underbody and an altered rear valance that help it to slip through the air with greater aerodynamic efficiency than petrol-engined versions of Ingolstadt's performance flagship.
New electric driveline
Beneath the familiar bodywork, however, lurks the new electric driveline technology showcased on the wheeled out at the , including a patented welding process for the 52 battery modules.
Hackenberg says this was pioneered on the and is claimed to vastly improve the thermal properties of the 7488 individual lithium-ion cells mounted behind the cabin for greater energy saving.
Adopting the same layout as the earlier R8 e-tron prototype we drove back in 2013, the new production version is driven by a pair of electric motors that act exclusively on the rear wheels.
However, while the original layout has been retained, each individual driveline component has been upgraded in a bid to provide the latest incarnation of Audi's electric sports car with added performance and a far more practical range.
The new electric motors, produced at parent company Volkswagen's Kassel manufacturing plant in Germany, deliver a combined 340kW, or some 60kW more than before. Torque has also increased by 100Nm to a new peak of 920Nm – all of which is unleashed the very moment your foot brushes the throttle.
To put this into some sort of perspective, the four-wheel-drive Tesla Model S P85D possesses 515kW and 931Nm. However, while the R8 e-tron is claimed to weigh 1840kg, the P85D hits the scales at 2100kg.
Heading for the coast
Drive from the e-tron's electric motors is channelled through a fixed-ratio gearbox. This has been modified to include a coasting function that sees the new Audi freewheel with minimal mechanical drag when you come off the throttle for extended periods – a function Hackenberg believes should have been included on the car from the outset.
Whereas the earlier R8 e-tron drew its electric energy from a 48.6kWh lithium ion battery, the new one gets a much larger 91.0kWh unit. The cells it uses also operate at a higher 3.6 amperes compared with 3.2 amperes previously, giving the e-tron greater discharge ability for improved accelerative performance.
As with the exterior, the e-tron's interior is based around the first-generation R8, albeit with a number of subtle changes. They include the instruments, which have been modified to reveal information relating to the electric driveline.
The standard electrically operated seats are also replaced by manually operated sports seats as part of a number of weight saving measures, including the use of carbon fibre in the otherwise aluminium body structure. The steering wheel adjusts for both rake and reach, so there is no problem finding a comfortable driving position.
Behind the wheel
To get underway you hit the starter button, draw the stubby gear lever back to 'D' and release the electronic hand brake, before gliding off. The throttle is quite heavily sprung, although it is linear in action and easily modulated in the first few degrees of travel, making the R8 e-tron easy to thread through urban traffic. Step-off performance is wonderfully muscular as the electric motors spool up.
There is a big red button within the centre console to activate a sound generator used to mimic the hum of the naturally aspirated 5.2-litre V10 direct-injection petrol engine used by the standard R8.
However, Hackenberg is not a fan of such frippery, preferring the distant whine of the electric motors and roar of the tyres on the bitumen to provide a sensation of speed, so it was turned off for our journey across Switzerland.
Owing to the tall battery pack behind the seats and the fact that, subsequently, the rear window is blanked off, the e-tron has a 6.8-inch AMOLED monitor in place of a rear-view mirror. Inspired by the unit used on the R18 e-tron quattro Le Mans race car, it carries real-time video captured by a rear view camera.
It's a little odd at first but you soon become accustomed to its shallow depth of field. Whether or not it appears on the production car is up in the air right now, says Hackenberg.
Plenty in reserve
At posted limits, the R8 e-tron always feels to have plenty in reserve. At typical motorway speeds solid performance is just a fleeting nudge of the throttle away. A heavy dose of right foot sees the hi-tech two-seater accelerate with terrific force as the prodigious torque is doled out to each rear wheel.
The R8 e-tron may tip the scales at 1840kg but the inherent response and sharpness of its acceleration gives the impression that it weighs a lot less. Its longitudinal stability is also exemplary, making it a pleasing car to steer over longer distances on the highway.
Audi claims this latest incarnation of its electric sports car is good for 0-100km/h in just 3.9sec. This is 0.7sec slower than the new 449kW 5.2-litre R8 V10 Plus but 0.3sec faster than Ingolstadt officials quoted for the initial R8 e-tron prototype we drove back in 2013.
And the Model S P85D Tesla claims a 0-100km/h time of 3.4sec, making it the king-of-the-hill as far as electric cars go right now.
The top speed of the new Audi is currently limited to 200km/h, although this is likely to be increased for the production car. What really grabs your attention, though, is the intensity of its acceleration, particularly in the 75-120km/h range, when you find a suitable stretch of road and gun it.
Superb traction, eager cornering
There is an agreeable amount of feedback from the electro-mechanical steering system and superb traction thanks to the use of a torque vectoring system, that splits the drive between the individual rear wheels. The handling is satisfyingly neutral, too.
The R8 e-tron corners eagerly with responsive turn-in traits, impressive grip and outstanding body control. Predictably, given the car's weight, the ride is rather firm. However, there is sufficient wheel travel to ensure it never feels uncomfortable.
The driver can choose between a recuperation mode, in which kinetic energy produced under braking is stored in the battery, or a coasting mode, which disconnects drive between the electric motor and gearbox to provide a freewheeling effect on a trailing throttle.
Meanwhile, a raft of readouts within the instrument binnacle allows you to keep close tabs on energy consumption and the state of the battery charge.
On a run of 230km over a combination of urban streets, secondary roads and highways on the way to Geneva last week, we used just three-quarters of the available electricity, averaging 19.9kWh per 100km. At the end of the journey the range-to-empty readout was showing 113km, suggesting Audi's revised 400 to 450km range claim is within reach under normal driving conditions.
Although billed as a prototype, the R8 e-tron we drove was exceptionally well engineered and boasted truly impressive levels of quality. If it is a signal of what is to come, the definitive production car that is planned for delivery by the end of the year not only promises to be one of the fastest accelerating but also one of the best built electric cars yet.