A lot has changed since we last tested Audi’s all-electric sports car, the e-tron.

Back in 2010 it was a four-wheel-drive, four-motor prototype that was destined for 1000-car per year production. It was set to receive distinct styling, its own spaceframe, a unique interior, a 1600kg kerb weight and due to be sold at “above R8” prices.

Now it’s a two-motor, rear-wheel-drive, 1780kg coupé prototype that’s based on the facelifted R8. Audi has developed and built 10 cars to a production standard, each valued at over £850,000, in a short space of time to demonstrate the technology and continue trials.

Opting for a rear-drive layout, instead of the quattro system found in normal R8s, may seem a somewhat counterintuitive move. Audi says, however, that the e-tron's rear-drive layout offers adequate traction, negating the need for four-wheel drive, and a more engaging driving experience. There would also be considerable packaging, weight and technical challenges to overcome using a quattro configuration.

The R8’s high-performance electric motors draw current from a 48.6kWh lithium-ion battery, the bulk of which sits behind the driver. Combined, the motors deliver 375.5bhp and 604.8lb ft. This allows the R8 e-tron to dispatch the 0-62mph sprint in 4.2sec and reach a limited top speed of 124.27mph. Derestricted it could reach over 155mph, at the cost of efficiency.

It’s not just the powertrain that’s different. The e-tron makes extensive use of carbonfibre, in order to bring its weight down to reasonable levels, and there are myriad cosmetic and technical changes. The braking system has undergone major revisions, while the motors allow for regenerative braking and an advanced form of torque vectoring.

One thing’s for sure: this is not a dull car. Press the start button and a bassy synthetic thrum fills the cabin. Select ‘D’ with the stubby gear lever, release the electronic handbrake and the R8 glides away.

Inside it's much like a conventional R8, barring instrumentation that shows power usage, levels and distribution. Snug bucket seats, which adjust only fore and aft, replace the standard items. The e-tron's steering wheel adjusts for rise and reach, however, so finding a comfortable driving position isn't too difficult.

What's most notable is the absence of a rear-view mirror. The tall battery pack obscures your view, so Audi has blanked off the rear glass and installed a 6.8-inch AMOLED display and rear-view camera. It feels slightly unnatural at first but you quickly acclimatise to it.

Squeeze the e-tron's throttle and, instantaneously, the electric motors spool and propel it forwards at a seemingly relentless rate. The throttle has a natural-feeling and linear response, impressive for an electric vehicle, while the braking system delivers barely perceptible transitions between regenerative and physical braking; there’s a phenomenal amount of stopping power on offer and engine braking can be simulated using the adjustable regeneration controls via the wheel-mounted paddles.

There’s a satisfying amount of feedback from the steering, assisted by being able to more easily hear what the tyres are doing, and the R8 corners in a flat fashion. Remarkably, it conceals its bulk well – 577kg of which is the battery – and never feels unwieldy or liable to break away unexpectedly. The ride quality is firm, predictably, but comfortable.

Audi’s torque vectoring system makes itself apparent in tighter, faster corners. As you perceive the car’s front end to be reaching the limit of adhesion, you’ll find that the nose tucks in hard and continues to travel in the desired direction. It’s a peculiar sensation but one that’s particularly gratifying, as you can feel the rear wheels being individually braked and accelerated to help maintain the desired line.

Because the artificially generated sound rises in pitch and volume with the road speed, and because the throttle operates in an intuitive fashion, it's easy to judge your control inputs. Making swift progress in the R8 e-tron feels delightfully natural as a result, and you very quickly forget that it's lacking an internal combustion engine.

As you’d expect, there’s plenty of grip and traction on offer but, with adjustable drive modes and stability control, the e-tron is more than happy to step its tail sideways. It’s thoroughly good fun yet it feels safe, controllable and quick – all while making its own unique noise. As with many high-performance Audis, it’s also effortlessly capable of flattering your own driving.

Equally satisfying is the depth of engineering in the R8 e-tron. Take, for example, the flaps in the apertures of the wheels. At speeds over 31mph they are forced closed, reducing the e-tron’s coefficient of drag by 0.02Cd. Drop below that speed and they open again, allowing more air to flow over the carbon-ceramic disc brakes.

The true benefit to the Audi R8 e-tron's acceleration and range capabilities is marginal at best, but it demonstrates the lengths that Audi is willing to go to in order to eke every ounce of performance and efficiency out of a car.

Despite having a claimed optimum range of 133.6 miles, and an acceptable charging time of less than one hour from a dedicated point, Audi was initially not happy with the limitations of the prototype that were enforced by its batteries.

It was an understandable concern. Driven at speed, Audi’s engineers said that the R8 e-tron prototype would deplete its battery in approximately 30 miles. Regardless of how good the car might be, it was a stumbling point that would put off many a customer – and it was one of the primary reasons Audi originally decided against selling the R8 e-tron.

Since the original test of the prototype, however, developments in battery technology have more than doubled the R8 e-tron prototype's range to 279 miles. Ulrich Hackenberg, Audi's board member for technical development, stated that progress in battery technology and a more space-efficient packaging for the batteries had resulted in the improvements.

No launch date for a production version has been announced yet – the car would most likely be built to order if it were to reach series production status – but Audi will continue to use it as a development test bed.

So, regardless of how much you might want one, you won't be able to lay your hands on an R8 e-tron for the duration. Nevertheless, it's a phenomenal piece of engineering, finished to an incredible standard, that shows what's possible using electric power.

If you want an electric car with supercar-threatening performance right now, then you could consider the Mercedes-Benz SLS Electric Drive. It costs approximately £302,000 plus taxes in left-hand drive markets and is claimed to sprint from 0-62mph in 3.9sec, before reaching a limited top speed of 155mph. Driven normally, it should prove capable of covering 155 miles on a single charge.

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