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Tesla ‘Roadrunner’ cell leak hints that Battery Day will be more insane than expected
Tesla’s Battery Day has been hyped so much that the event will have to include something truly amazing to live up to its expectations. In the lead up to the highly-anticipated event, a leaked image featuring what is supposedly a cell from Tesla’s “Roadrunner” line has emerged. And if the leak proves legitimate, it would appear that Battery Day will not only meet expectations — it will be even more insane than expected.
The leaked image, which was initially published in a report on Electrek, featured a massive battery cell that was supposedly a product of the Roadrunner line. The publication noted that the image was sent through an anonymous source and confirmed by another independent source. From the get-go, it is evident that the cell is massive, closer in size to a supercapacitor than a traditional battery cell. Initial observations by battery enthusiasts online also point to some radical improvements that such a cell design would bring.
While Electrek’s sources have mentioned that the Roadrunner cell will feature roughly double the diameter of the 2170 cells that the electric car maker currently uses in the Model 3 and Model Y, Tesla enthusiast @_BRCooper, who is familiar with battery tech, has observed that one of the leaked images had the number “054” printed on its side. If this number represents the cell’s diameter, it would point to Tesla’s Roadrunner cells adopting a 54×98 form factor, which has 10x the volume of a 2170 cell.
As noted by Jordan Giesige of The Limiting Factor channel on YouTube, adopting a 54×98 form factor for its next-generation cells has numerous implications for the entire battery manufacturing process and the performance of Tesla’s vehicles as a whole. With the larger cells, Tesla could produce battery packs that have an order of magnitude fewer cells than before. This would result in the company only using 1/10 the number of rolls, cans, electrolyte fills, and welds compared to its current operations. Such a strategy opens the doors to massive cost reductions that could help bring down the prices of electric cars to a notable degree.
But regardless of its actual size, the design of the Roadrunner cell appears to be optimized and designed for a cell-to-pack drop-in setup. Interestingly enough, the leaked image of the Roadrunner cell seems to have a tabless electrode design, which Elon Musk has dubbed is “way more important than it sounds” last year. Provided that the Roadrunner cells are indeed inspired by Tesla’s tabless electrode patent, the new form factor could pave the way to more performance and further reductions in production costs.
What’s even more notable is that these improvements become possible with just the Roadrunner cell’s new form factor and design. Giesige, for his part, has noted that with the Roadrunner cell’s design and potential 54×98 form factor alone, Tesla may be able to close in on 300 wh/kg before making any significant changes to its battery chemistry. Elon Musk actually mentioned a 30-40% improvement from 250 wh/kg back in 2018, which translates to an improvement to 325-350 wh/kg. Musk’s prediction was considered fantastical by critics then, but as Battery Day approaches and leaks start to emerge about the event, it is starting to look more and more likely that 325-350 wh/kg is feasible.
Watch a feature on the Roadrunner battery cell leak in the video below.
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Tesla hosts Rome Mayor for first Italian FSD Supervised road demo
The event marked the first time an Italian mayor tested the advanced driver-assistance system in person in Rome’s urban streets.
Tesla definitely seems to be actively engaging European officials on FSD’s capabilities, with the company hosting Rome Mayor Roberto Gualtieri and Mobility Assessor Eugenio Patanè for a hands-on road demonstration.
The event marked the first time an Italian mayor tested the advanced driver-assistance system in person in Rome’s urban streets. This comes amid Tesla’s push for FSD’s EU regulatory approvals in the coming year.
Rome officials experience FSD Supervised
Tesla conducted the demo using a Model 3 equipped with Full Self-Driving (Supervised), tackling typical Roman traffic including complex intersections, roundabouts, pedestrian crossings and mixed users like cars, bikes and scooters.
The system showcased AI-based assisted driving, prioritizing safety while maintaining flow. FSD also handled overtakes and lane decisions, though with constant driver supervision.
Investor Andrea Stroppa detailed the event on X, noting the system’s potential to reduce severe collision risks by up to seven times compared to traditional driving, based on Tesla’s data from billions of global fleet miles. The session highlighted FSD’s role as an assistance tool in its Supervised form, not a replacement, with the driver fully responsible at all times.
Path to European rollout
Tesla has logged over 1 million kilometers of testing across 17 European countries, including Italy, to refine FSD for local conditions. The fact that Rome officials personally tested FSD Supervised bodes well for the program’s approval, as it suggests that key individuals are closely watching Tesla’s efforts and innovations.
Assessor Patanè also highlighted the administration’s interest in technologies that boost road safety and urban travel quality, viewing them as aids for both private and public transport while respecting rules.
Replies on X urged involving Italy’s Transport Ministry to speed approvals, with one user noting, “Great idea to involve the mayor! It would be necessary to involve components of the Ministry of Transport and the government as soon as possible: it’s they who can accelerate the approval of FSD in Italy.”
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Tesla FSD (Supervised) blows away French journalist after test ride
Cadot described FSD as “mind-blowing,” both for the safety of the vehicle’s driving and the “humanity” of its driving behaviors.
Tesla’s Full Self-Driving (Supervised) seems to be making waves in Europe, with French tech journalist Julien Cadot recently sharing a positive first-hand experience from a supervised test drive in France.
Cadot, who tested the system for Numerama after eight years of anticipation since early Autopilot trials, described FSD as “mind-blowing,” both for the safety of the vehicle’s driving and the “humanity” of its driving behaviors.
Julien Cadot’s FSD test in France
Cadot announced his upcoming test on X, writing in French: “I’m going to test Tesla’s FSD for Numerama in France. 8 years I’ve been waiting to relive the sensations of our very first contact with the unbridled Autopilot of the 2016s.” He followed up shortly after with an initial reaction, writing: “I don’t want to spoil too much because as media we were allowed to film everything and I have a huge video coming… But: it’s mind-blowing! Both for safety and for the ‘humanity’ of the choices.”
His later posts detailed FSD’s specific maneuvers that he found particularly compelling. These include the vehicle safely overtaking a delivery truck by inches, something Cadot said he personally would avoid to protect his rims, but FSD handled flawlessly. He also praised FSD’s cyclist overtakes, as the system always maintained the required 1.5-meter distance by encroaching on the opposite lane when clear. Ultimately, Cadot noted FSD’s decision-making prioritized safety and advancement, which is pretty remarkable.
FSD’s ‘human’ edge over Autopilot
When asked if FSD felt light-years ahead of standard Autopilot, Cadot replied: “It’s incomparable, it’s not the same language.” He elaborated on scenarios like bypassing a parked delivery truck across a solid white line, where FSD assessed safety and proceeded just as a human driver might, rather than halting indefinitely. This “humanity” impressed Cadot the most, as it allowed FSD to fluidly navigate real-world chaos like urban Paris traffic.
Tesla is currently hard at work pushing for the rollout of FSD to several European countries. Recent reports have revealed that Tesla has received approval to operate 19 FSD test vehicles on Spain’s roads, though this number could increase as the program develops. As per the Dirección General de Tráfico (DGT), Tesla would be able to operate its FSD fleet on any national route across Spain. Recent job openings also hint at Tesla starting FSD tests in Austria. Apart from this, the company is also holding FSD demonstrations in Germany, France, and Italy.
Tesla Optimus showed off its newest capability as progress on the project continues to accelerate toward an ultimate goal of mass production in the coming years.
Tesla is still developing Optimus and preparing for the first stages of mass production, where units would be sold and shipped to customers. CEO Elon Musk has always marketed the humanoid robot as the biggest product in history, even outside of Tesla, but of all time.
He believes it will eliminate the need to manually perform monotonous tasks, like cleaning, mowing the lawn, and folding laundry.
However, lately, Musk has revealed even bigger plans for Optimus, including the ability to relieve humans of work entirely within the next 20 years.
JUST IN: Elon Musk says working will be ‘optional’ in less than 20 years because of AI and robotics. pic.twitter.com/l3S5kl5HBB
— Watcher.Guru (@WatcherGuru) November 30, 2025
Development at Tesla’s Artificial Intelligence and Robotics teams has progressed, and a new video was shown of the robot taking a light jog with what appeared to be some pretty natural form:
Just set a new PR in the lab pic.twitter.com/8kJ2om7uV7
— Tesla Optimus (@Tesla_Optimus) December 2, 2025
Optimus has also made several public appearances lately, including one at the Neural Information Processing Systems, or NeurIPS Conference. Some spectators shared videos of Optimus’s charging rig, as well as its movements and capabilities, most interestingly, the hand:
You have to hand it to Elon 🤟 pic.twitter.com/fZKDlmGAbe
— Ric Burton · NeurIPS 2025 (@_ricburton) December 2, 2025
The hand, forearm, and fingers have been one of the most evident challenges for Tesla in recent times, especially as it continues to work on its 3rd Generation iteration of Optimus.
Musk said during the Q3 Earnings Call:
“I don’t want to downplay the difficulty, but it’s an incredibly difficult thing, especially to create a hand that is as dexterous and capable as the human hand, which is incredible. The human hand is an incredible thing. The more you study the human hand, the more incredible you realize it is, and why you need four fingers and a thumb, why the fingers have certain degrees of freedom, why the various muscles are of different strengths, and fingers are of different lengths. It turns out that those are all there for a reason.”
The interesting part of the Optimus program so far is the fact that Tesla has made a lot of progress with other portions of the project, like movement, for example, which appears to have come a long way.
However, without a functional hand and fingers, Optimus could be rendered relatively useless, so it is evident that it has to figure this crucial part out first.
Tesla hosts Rome Mayor for first Italian FSD Supervised road demo
Tesla FSD (Supervised) blows away French journalist after test ride
