The Nardò high-speed ring in southern Italy is a place where cars go to prove themselves. It’s a 7.8-mile circle of asphalt, banked just right so a car can hold triple-digit speeds without constant steering corrections. This summer, it became the stage for one of the most audacious EV tests ever attempted. Mercedes-AMG’s Concept GT XX EV ran at 186 mph (300 km/h) nearly nonstop for more than a week, covering 25,000 miles in 7 days and 14 hours, with the run completing on August 25, 2025. By the time the dust settled, it had set 25 endurance records and logged enough distance to circle the globe.
The Car That Redefined Endurance
The GT XX is a four-door electric super sedan built on Mercedes-AMG’s new AMG.EA platform. It uses a tri-motor layout: two axial-flux motors at the rear for continuous power, and a booster motor at the front to deliver on-demand performance. Together, they produce 1,360 hp, making it the most powerful AMG car ever engineered. Unlike most EVs, it could sustain this power for days without cutting output.
The battery system is just as radical. Using 3,000+ cylindrical NCMA cells, each immersed in oil for direct cooling, the pack maintained performance across extreme loads. This cooling method kept cell temperatures balanced even as the cars circled Nardò at 186 mph through heat and rain. Operating at 800V, the battery accepted up to 950 kW peak charging, which translated to 250 miles of range in 5 minutes, a benchmark no production EV has touched.
Mercedes CTO Markus Schäfer emphasized that this wasn’t just an experiment: “We’re the first manufacturer to use axial-flux motors and directly cooled batteries in a production-intent EV, and this test shows exactly why. This technology is going into our customer cars.”
The Purpose Behind the Test
Mercedes-AMG set out to prove more than just raw numbers. The goal was to validate the new AMG.EA platform in the harshest possible conditions. AMG calls the GT XX a “marathon sprinter”, a car that can deliver supercar performance repeatedly without overheating or throttling back. CEO Michael Schiebe explained: “Unlike other performance EVs, the GT XX is not just a sprinter. It’s a marathon sprinter.” That distinction framed the entire run: AMG wanted to show consistency, not one-off speed.
The symbolic element mattered too. The engineers dubbed the project “around the world in eight days,” tying the effort to the distance of Earth’s circumference. It was both a marketing hook and a way to measure whether their technology could truly endure.
The Execution: Racing the Clock
The test involved two GT XX prototypes and 17 drivers working in shifts. Stints lasted about two hours each, echoing the rhythm of endurance racing. Drivers included Mercedes-AMG F1’s George Russell, F1 Academy driver Doriane Pin, and Fabian Vettel. Russell later noted: “The axial flux motors respond as immediately and precisely as a Formula 1 drivetrain, but with endurance I’ve only ever felt in combustion engines.”
The cars logged 3,177 laps each on Nardò’s steeply banked outer ring. Nardò was chosen because its banking allows cars to maintain extremely high speeds without constant steering corrections. The facility also provided the infrastructure for prototype megawatt-class chargers to be installed trackside.
During the week, daytime temps climbed to 95°F (35°C), with the track surface soaring to 160°F (71°C). Nighttime rain slicked the surface, but neither car faltered. The direct oil cooling of both motors and batteries meant there was no power fade, even after days of continuous output. Pit crews managed tire swaps, driver changes, and charging stops with the precision of a 24-hour race team. Tire wear was closely monitored, as the banking placed heavier loads on the outer shoulders. Multiple sets of specially developed Michelin endurance tires were cycled in to keep grip consistent.
Charging stops became the rhythm of the event. While one car charged, the other stayed on track, ensuring constant progress. With charging speeds sustained around 850 kW, pit stops lasted minutes instead of hours. Engineers optimized charge windows, avoiding the slow final 10 percent of the battery and keeping the pack in its most efficient state-of-charge range. Telemetry streamed data in real time, from cell temperatures to tire pressures. The engineering team adjusted strategy on the fly, balancing speed and charging downtime to keep average speed as high as possible.
Breaking Down the Records
The GT XX didn’t just edge out old marks, it obliterated them.
- 24 Hours: 5,479 km (3,405 miles), nearly 1,000 miles farther than XPeng’s 2025 record.
- 48 Hours: 10,860 km (6,750 miles).
- 72 Hours: Over 16,000 km (10,000+ miles).
- 7 Days: 37,260 km (23,160 miles).
- Earth Circumference: 40,075 km (24,901 miles) in 7 days, 13 hours, 24 minutes.
- Total Run: 25,000 miles (40,268 km) in 7d 14h.
To put that in perspective, the GT XX essentially ran ten back-to-back Le Mans 24-hour races at speeds faster than most winning entries. Including pit stops, the average speed was 137 mph (220 km/h). While moving, the cars stayed fixed at 186 mph.
The Technology That Made It Possible
Axial-Flux Motors: Compact, power-dense units that delivered continuous performance thanks to oil cooling. The tri-motor layout gave flexibility: two rears doing the heavy lifting, with the front “booster” stepping in when traction or extra thrust was needed.
Direct-Cooled Battery: Every cell bathed in coolant meant no thermal runaway, no derating, and no sag in performance after repeated charge cycles. The cells used NCMA cathodes with silicon-anode chemistry, housed in lightweight aluminum cases for better cooling and weight reduction.
Ultra-Fast Charging: Prototype chargers from Alpitronic delivered near-megawatt charging, shrinking pit stops to minutes. Five minutes added around 400 km of range. Charging currents approached 1,000 amps, something no current production EV supports.
Aerodynamics: Active aero surfaces, including Bluetooth-controlled active aero wheels, adjusted to reduce drag and improve stability on Nardò’s banked track. At 186 mph for days on end, these small adjustments reduced strain on tires and improved efficiency.
Michelin Endurance Tires: Special compounds designed for high sustained speeds rotated in regularly, coping with asymmetric wear from the banking.
Energy and Efficiency
At first glance, sustaining 186 mph for days seems like it would drain energy uncontrollably. Yet the GT XX managed roughly 280 Wh per mile at that pace, better than expected for a car moving against air resistance that rises with the cube of speed. Over 25,000 miles, each car consumed around 40 MWh of electricity, a figure equivalent to what a small town might use over the same period.
Engineers deliberately targeted 186 mph as the sweet spot. At higher speeds, drag would skyrocket and demand more charging stops. At lower speeds, efficiency would improve, but total distance per day would drop. By holding 186 mph and leveraging ultra-fast charging, AMG found the balance that maximized net distance.
Maintenance and Strategy
The run wasn’t just about speed, it was also a masterclass in endurance racing logistics. Tires wore unevenly due to the banking, with outer shoulders taking the brunt of the load. Crews swapped sets at regular intervals, just as in a 24-hour race. Each stop also gave engineers a window to inspect components, review telemetry, and adjust strategy.
Telemetry wasn’t just for monitoring, it actively shaped decisions. Battery temperatures, inverter load, and motor oil temperatures dictated when cars would pit and how long they’d charge. The team avoided topping the battery to 100 percent to skip the slower charge taper, instead running it in the middle bands for faster turnaround. This strategy meant that even with multiple stops, the cars averaged 137 mph across the week.
The execution showed AMG’s motorsport DNA. Everything was handled with pit-lane precision, from plugging in megawatt chargers to swapping tires in blistering heat. The fact that both cars finished within 15 miles of each other after 25,000 shows just how disciplined and consistent the operation was.
Megawatt Charging Record
In the week after the endurance run, Mercedes-AMG demonstrated that the GT XX could also set records at the charging station. At a prototype unit developed with Alpitronic, the car reached a peak of 1,041 kW, breaking the one megawatt barrier. That figure was achieved just 0.5 seconds after plugging in and was held steady for around two and a half minutes. During that time, up to 1,176 amps flowed through a specially designed CCS cable, delivering 17.3 kWh in a single minute. On paper, that equals about 125 km (78 miles) of WLTP range per minute.
The pack itself uses tall, slim NCMA cylindrical cells with energy density over 300 Wh/kg, housed in laser-welded aluminum cases for efficient current and heat transfer. More than 3,000 cells are directly cooled by electrically non-conductive oil to keep temperatures uniform. Operating at more than 800 volts, the design reduces weight and shortens charge times, while intelligent thermal management ensures stability under megawatt loads. Mercedes emphasized that this is the same battery architecture heading into series production on AMG.EA.
The charging hardware was just as innovative. An MCS truck charger was reworked to support a slimmer CCS cable while still carrying megawatt-level current. Mercedes-Benz and Alpitronic plan to adapt the lessons learned here into a new generation of high-performance fast chargers available at Mercedes-Benz charging parks in Europe and North America from 2026.
Final Thoughts
The AMG GT XX EV’s endurance run at Nardò validated AMG’s most ambitious engineering yet. It tested the limits of motors, batteries, tires, and drivers under conditions harsher than any owner will face. By combining record-breaking results with a deliberate philosophy that electric cars must sprint and endure, Mercedes-AMG has redefined expectations. The next wave of AMG models won’t just be fast. They’ll be built to go the distance.
