Does the competitor who crosses the finish line first reach the highest peak speed, or the one who maintains a higher average speed from start to finish? Easy answer: the second one wins. Outside the metaphor, the finish line is the restoration of a good battery charge level — let's say 80 per cent of maximum capacity. The competitor is the electric car that needs to recharge. To be first under the imaginary chequered flag, there are many approaches: the one studied — and continually refined — by the Volkswagen Group focuses entirely on consistent performance while the plug is connected to the car.

From 5 to 70 per cent charge at maximum power

Before understanding how a high charging power can be sustained for a long time, let's look at some figures. 150, for instance, which corresponds to the maximum charging power in kW available to the Audi e-tron 55 when connected to an HPC (High Power Charging) station. As those in the know will be aware, there are brands that have gone further, reaching peak figures of 200 kW. Values that, however, say very little when taken in isolation. What matters enormously is the car's ability to sustain high power levels for an extended period. And this is where Audi's system makes the difference: from 5 per cent all the way to 70 per cent of battery capacity, charging power remains consistently above 140 kW.

45 minutes and charging is done

With figures like these, the Audi e-tron 55 sees its batteries (with a nominal capacity of 95 kWh) charged to 100 per cent in just 45 minutes. Competing models, according to Audi's measurements, require twice as long: 91 minutes. This is because, despite a peak close to 200 kW, the battery management electronics already reduce charging power after just ten minutes. At the thirteenth minute it stands at around 140 kW (the same as Audi's), and by the twenty-third minute it is significantly lower: 80 kW, compared, once again, to the e-tron's 140 kW.

Liquid cooling for the batteries

To deliver their best, batteries must operate at temperatures between 25°C and 35°C. Above and below this range, not only does performance drop, but long-term durability is also compromised (over time, of course, not as a result of a single episode). And the further one moves from the 25°C–35°C range, the more the negative effects are amplified. To address all of this, Audi has developed a battery pack cooling system that relies on twenty-two litres of coolant and forty metres of tubing divided into four circuits. This allows the heat that inevitably builds up during high-power charging — due to the battery's internal electrical resistance — to be dissipated.

A refreshing "bed"

Technically, it is the cooling unit that eliminates the excess heat, and this unit is in turn bonded to the lithium battery housing. The bonding is achieved using a thermally conductive sealing gel, which transfers the heat generated by the cells uniformly. This architecture has also been designed with an eye to impact resistance.

Faster is better. For the individual and for society

All of this, it should be noted, does not exhaust its significance within the realm of engineering competition: it has practical implications in everyday life. Imagine having to tackle a long journey: if charging times are halved, the journey itself is shorter. More than that: when it comes to deciding whether or not to buy an electric car, knowing that it can be used over long distances is undoubtedly a powerful purchase incentive — with all the easily imaginable benefits, should this choice spread to a truly large number of drivers.