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Tesla ‘Roadrunner’ cell leak hints that Battery Day will be more insane than expected

Tesla Gigafactory Nevada battery cell production line (Credit: Super Factories)

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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. 

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Watch a feature on the Roadrunner battery cell leak in the video below. 

Simon is an experienced automotive reporter with a passion for electric cars and clean energy. Fascinated by the world envisioned by Elon Musk, he hopes to make it to Mars (at least as a tourist) someday. For stories or tips--or even to just say a simple hello--send a message to his email, simon@teslarati.com or his handle on X, @ResidentSponge.

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Elon Musk

How to use Grok Bot to block spam calls and texts

Musk told users to ask Grok Bot to scrub their phone numbers from spam lists.

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Elon Musk has a new use case for Grok Bot, and it is the spam call. On Thursday he replied to an X user named Arash with a short instruction: “Ask your @Grok @Bot to remove your phone number from spam call & text lists!” Arash had said he got tired of the calls, had an AI bot find his number on listing sites and file removal requests, and packaged the process as a free skill for others.

The skill is called Spam-Call Scrubber, which is described to find a phone number on people search sites and data brokers, submits the opt outs, completes the confirmation emails those sites send back, and rechecks on a schedule the user picks. Using it requires the Grok Bot app. The pitch is time saved, since most broker opt outs sit behind separate forms on separate sites.



Musk said Grok Bot now gives each bot its own email address, and that it can detect scam emails. On Thursday he also said SpaceX would make users whole if the bot botches a purchase or leaks a card, then told users to shop away from Amazon after the retailer blocked the agent, as Teslarati reported. The terms of service we reviewed at the time put responsibility for what an agent does on the user.

For Tesla owners, Grok Bot is not just a phone app. Tesla brought Grok Bot into its vehicles on September 22, and we argued earlier this week that the Cybercab’s real advantage may be the errands it runs during a ride. Every Cybercab and the rest of the Model Y Robotaxi fleet has it enabled. The more routine tasks like this one become, the more a rider has reason to hand over something personal in the back seat.

The new Spam-Call Scrubber skill can be downloaded for free and works on sites that honor removal requests, while noting that listings can reappear, and illegal robocallers do not check any registry. Whether Spam-Call Scrubber cuts anyone’s call volume is something the first wave of users will find out, and Musk’s endorsement guarantees that wave is coming.

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Investor's Corner

Tesla’s flying Roadster just revealed something bigger than the car

Analysts say the Roadster demo puts a Tesla and SpaceX merger back on the table.

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Tesla’s new Roadster, upside down and trailing cold gas thruster smoke, flips over a lineup of Tesla vehicles at the Roadster unveiling near Waco, Texas on October 15, 2026. (Image: Tesla)
Tesla’s new Roadster, upside down and trailing cold gas thruster smoke, flips over a lineup of Tesla vehicles at the Roadster unveiling near Waco, Texas on October 15, 2026. (Image: Tesla)

The Roadster unveiling near Waco ended Thursday night, and by Friday morning much of the investor reaction had less to do with the car than with who owns the rocket technology inside it.

Wedbush analyst Dan Ives said the event “puts the Tesla/SpaceX relationship on the table in a tangible way,” pointing to the propulsion, pressure vessel and control hardware sitting on a Tesla product. Gene Munster of Deepwater Asset Management called the demo “a ridiculous display of engineering” with “no commercial value” beyond embarrassing traditional automakers, though he said it showed Musk wants the two companies together.

The more specific forecast came a day earlier from Barclays. Analyst Dan Levy told clients a deal could be announced before Tesla’s annual meeting, which must happen by December 6, and that an announcement in late October or early November could make shareholder approval harder. Barclays expects SpaceX to be the buyer in an all stock deal, with Tesla holders receiving SpaceX shares at a premium, based on market values of roughly $2.1 trillion for SpaceX and $1.5 trillion for Tesla. If nothing lands around the meeting, the bank still sees an announcement within 6 to 12 months.

The Roadster demo just added more weight to merger speculations. Tesla’s demo used cold gas thrusters and pressure tanks of the kind SpaceX uses on Falcon 9, and Musk described the car as a collaboration between Tesla and SpaceX engineers, as we mentioned in our breakdown of the three Roadster configurations.


Musk has not publicly addressed a deal since the event, as far as we have seen. His most direct answer remains the one he gave at the All In Summit, when he said that with so much collaboration, “who can imagine what action one might take” without ruling anything out. Ives has held to a 2027 timeline since his March note, and Musk pushed back on the China piece of the speculation when ARK floated a year end announcement in August.

The next test is Tesla’s third quarter earnings call on October 21. However, we recall in July that Musk told analysts, “we can’t talk about combining companies and that kind of thing on an earnings call,” so a clear answer wouldn’t be expected.

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How Tesla’s Roadster fan system and thrusters are built to dominate the corners

Tesla’s Roadster uses fans, active wings and cold gas thrusters to create grip at any speed.

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The Roadster’s rear wing, one of the aerodynamic elements Tesla pairs with a fan-based downforce system. (Image: Tesla)
The Roadster’s rear wing, one of the aerodynamic elements Tesla pairs with a fan-based downforce system. (Image: Tesla)

Tesla’s new Roadster is best known for flipping through the air in Texas, but the technology that matters most for a race track is the stuff that keeps it on the ground. Tesla’s Roadster page describes a multi-mode fan and ground sealing system that acts as a downforce generator, pulling air out from beneath the car. Tesla says it provides enough suction to hold the vehicle upside down, even when stationary.

That is the key difference from the wings and diffusers on a normal supercar. Conventional aero only makes downforce when the car is moving, and it grows with speed, so a car has the least grip in the slow corners and under hard braking. A fan system makes downforce at any speed. Tesla’s patent, which we covered last year, describes fans and deployable skirts that create sealed or partially sealed regions under the car, with the fans extracting air to lower the pressure and increase grip and stability.


Tesla pairs that with active wings, a next generation steer by wire system and a Track Mode that lowers the car and changes the suspension, with high downforce and low drag settings for the circuit. To keep weight down, Tesla points to magnesium, titanium and carbon fiber, manual controls and a fixed seat position, which it says lets the car respond to driver inputs almost instantly.

Tesla Roadster: Three configs, one can fly, 0-60 in 0.8 seconds

The cold gas thrusters are the other half. On the Thrust version they sit at the rear and Tesla says they take the car from 0 to 60 mph in under 0.9 seconds, while the Rocket version adds perimeter thrusters for forward, upward and lateral rotational movement. Tesla says the all electric actuators make micro adjustments within a fraction of a second.


Musk has been talking about records for years. In June 2019 he said, “We’re going to do things with the new Roadster that are kind of unfair to other cars.” That September, when a follower asked whether the Roadster would beat the Nürburgring production car record, he replied with one word, “Absolutely,” as we reported at the time. In February 2024 he said Tesla had “radically increased the design goals” for the car and that its sub one second 0 to 60 time would be “the least interesting part.”

There are caveats. Tesla has not published a lap time or a verified cornering figure, so the record talk is still a promise rather than a result. Tesla also says the car is not approved for public road use, and the thruster features are limited to the Rocket trim, which is invite only. Fan cars have also been banned or withdrawn before, and getting a sealed underbody to work on a rough public road is a harder problem than on a smooth track. The first real test will be an official lap at a circuit.

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