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Understanding the Tesla 12V Battery Service Warning

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During the time when I was sitting on the sideline waiting patiently for delivery of my Model S, I read up on pretty much anything and everything related to the vehicle. I remember reading about 12V battery failures on the Model S, something Elon himself even commented on during one of the earnings calls.

RELATED: Tesla Model S 12V Lithium-Ion battery replacement (up to 70% lighter, 4x life)

It was reported that Tesla had chosen a poor vendor for the 12V battery which impacted early Model S owners but apparently this issue is still happening across later production vehicles. My Model S as well as several others that I personally know of received the 12V battery service indicator. For me this took place after 7 months and 18,000 miles of ownership.

Purpose of the Tesla 12V battery

Model S Battery

Tesla Model S 12V Battery (source: TMC forum)

The 12V battery in the Model S performs many of the same duties as it would in any internal combustion engine (ICE) car.The connections to the 12V battery on a Model S appear to be a bit more complex than in a traditional ICE as seen in the following picture (source: TMC forum).

RELATED: Why Tesla’s lead acid 12V battery needs to be lithium-ion based

The 12V battery maintains power for critical systems when the main battery pack is damaged or disabled. It powers the hazard lights, airbags, door locking and unlocking operations, as well as other critical componets of the Model S. The 12V battery also ensures that electronics are “awake” and listening to the key FOB in order to automatically lock and unlock the vehicle based on proximity. It also allows the car to maintain its 3G connection for remote access when the rest of the vehicle is powered off. If the 12V battery happens to fail, it will isolate the main battery pack from the car and prevent charging. This is a safety feature of the Model S designed to help protect first responders in the event of an accident.

What does my warning mean?

The “12V Battery Needs Service” warning can indicate a number of problems and the only way to truly understand the reason for the alert is to call Tesla Service (they’re available 24×7) and have them pull the logs. This is something that Tesla service can diagnose remotely.

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Tesla 12V battery terminal

Tesla 12V battery terminal

In severe cases Tesla Service will tell you to stop driving the car, but generally it’s an indication that the voltage level has dropped below a certain threshold but the vehicle can continue to operate normally until replaced. In the rare event that the the 12V battery dies while driving, the car will become disabled and will require a jump start to power on again. Our friend Kman has a good video on getting access to the terminals behind the nosecone to jump start the 12V, but please consult Tesla service and take caution before attempting this on your own.

Depending on the severity of the issue, there may be a 2-3 week lead time before Tesla Service replaces the 12V battery.

Many owners manage to get the battery replaced quickly, but in my case a busy Tesla Service Center combined with the fact that it was Thanksgiving holiday during a snowy New England week, had me driving with the warning light on for almost 2 weeks (about 1,000 miles) without encountering any issues.

Another interesting point to note is that Tesla may call you before you even see 12V battery service warning. Multiple owners have reported this proactive stance in advance of a warning which is great to see. Evidently Tesla’s early warning threshold is supersedes the trigger that kicks off the dash indicator.

Why are the 12V batteries failing?

Some owners are on their 3rd 12V battery already. Many others are reporting failures at the 1 year mark. In ICE cars you can normally expect about 4 years of life before needing to replace the 12V battery which begs the question – why are Tesla 12V batteries failing?

Some of the failures have been in the DC to DC converter that charges the 12V battery through the main battery pack. That converter can be seen as an equivalent to the alternator in your traditional ICE car. However, this doesn’t seem to be the main cause of the 12V battery failures. Current conjecture is that vampire load and the excessive strain on the 12V are causing the reliability issues.

Tesla may have a lingering design issue in their use of the 12V battery.

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From my reading, I think they upgraded the quality of the battery in the earlier models but we’re still facing the same underlying design issue in the way the 12V is stressed. Can Tesla fix the way the 12V battery is used with software updates alone? We don’t know, but fortunately they’re taking care of all of the replacements in the meantime. Unless they can address it remotely via software updates, there could be a factory “recall” brewing (and I use this term loosely).

Either way, Tesla should be more upfront about these issues and let owners know what they’re doing to address the underlying problem.

Getting the 12V battery serviced

From everthing I’ve heard and experienced through my own Model S, the replacement including labor and parts is 100% covered by Tesla.

Tesla Service can handle the replacement at your location, but given the poor weather conditions here in New England, I opted to have them pick up my Model S and do the replacement in the comfort of their own Service Center. They were able to service it within the same day, and to Tesla fashion they also updated/fixed a bunch of other minor things for free, while at it.

Summary

The 12V battery is a relatively inexpensive part in the Model S and is fairly simple to replace, but the bigger concern is why they seem to be failing so quickly. It isn’t a major issue for now but certianly something we should continue monitoring as concerned Model S owners.

I’ve started a poll over on TMC to see what kind of failure rate we’re seeing on the 12V battery so feel free to contribute to it or use it as a way monitor progress. So far over 75% of respondents have had their 12V battery replaced within 2 years.

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"Rob's passion is technology and gadgets. An engineer by profession and an executive and founder at several high tech startups Rob has a unique view on technology and some strong opinions. When he's not writing about Tesla

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Elon Musk

Elon Musk drops a surprise update on Boring Company’s next big dig

Musk says Boring Company could shrink the Austin to San Antonio drive to just minutes.

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Elon Musk says The Boring Company is working on what he called “a simple, precursor Hyperloop” tunnel connecting Austin and San Antonio, targeting speeds above 200 mph and cutting a drive that can take up to two and a half hours down to a consistent under 30 minutes. Musk posted the idea on X Sunday, in a reply to a repost of an AI generated video imagining a science fiction future with human colonies on other worlds, which he shared with the line “This is the future we shall bring into being.”


The Boring Company’s own account picked up the idea in the same thread, adding a detail about how the trip would actually work: “Because Loop/Hyperloop is express (i.e. no intermediate stops), one could travel from an Austin parking lot to a favorite San Antonio restaurant in about 30 minutes. As long as they both have Loop stations.” That framing ties the proposed intercity link to the same station model the company already runs in Las Vegas, where riders enter the tunnel network through small, garage style stops rather than one central terminal.

This is not the company’s first run at the Austin to San Antonio corridor. Boring Company floated tunnels between the two cities as far back as 2021, and later competed for a separate San Antonio Loop project tied to the airport before that specific bid stalled. Pitches for tunnels in Chicago, Los Angeles, and a New York to Washington corridor have followed a similar pattern of big announcement without a shovel in the ground.

What is different this time is the balance sheet, especially since The Boring Company closed a 3 billion dollar funding round led by investors in the United Arab Emirates earlier this month at a valuation near 23 billion dollars, giving the tunneling company more capital to chase speculative projects than it had during its earlier Texas pitches. The company is also mid-build on two other intercity systems it has actually broken ground on, inc;luding a Nashville tunnel linking downtown to the airport, where a second boring machine finished commissioning in June, and its Las Vegas network, where the station count keeps climbing on paper faster than tunnels get dug.

That gap between announcement and execution is the reason to treat Sunday’s post as an opening bid rather than a project. A tunnel spanning roughly 80 miles between two metro areas, running at speeds Boring Company has not demonstrated over any real distance, would dwarf anything the company has built. For now, the Austin to San Antonio Hyperloop exists as a caption under an AI generated space video.

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Tesla eyes supply partners for Optimus mass production

Tesla certified three Chinese suppliers for Optimus mass production, signaling its robot timeline is accelerating.

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Concept rendering of Tesla Optimus in mass production

Tesla’s robotics team traveled to Ningbo, in China’s Zhejiang province, on September 16 and spent the following day auditing component suppliers for Optimus, according to a Bloomberg report cited by RobotAIGeek. The visit moved three manufacturers from provisional status to certified mass production partners: Tuopu Group, which handles actuators and chassis components, Ningbo Joyson Electronic, a sensor supplier, and Zhejiang Sanhua Intelligent Controls, which builds thermal management systems. All three already supply parts to Tesla’s electric vehicles, and the audit reportedly came with fresh orders that supply chain reports put at an initial batch of roughly 5,000 units.

Tuopu, Joyson, and Sanhua built their manufacturing base serving the automotive industry, where tolerances and volume requirements are already close to what a mass produced humanoid robot demands. Sanhua in particular has history here. Teslarati reported last October that the company had received a roughly $685 million order for linear actuators tied to Optimus, a volume industry watchers estimated could cover around 180,000 robots once production ramped.

Supply chain reports tied to this week’s audit put Tesla’s near term production goal at about 1,000 Optimus units a week by late September, rising to 2,000 to 2,500 units a week by the end of the year. That pace would put real weight behind the timeline Tesla has been building toward since May, when it wound down Model S and Model X production at Fremont to convert that floor space into a dedicated Optimus line targeting one million units annually. JPMorgan analysts who toured the factory in August confirmed the conversion took roughly four months, a pace Musk has called unprecedented for a facility that size.

New drone video shows Tesla’s Optimus Factory reaching a turning point

Fremont is only the first phase. A second, larger Optimus plant is rising at Gigafactory Texas, where drone footage shared by Joe Tegtmeyer last week showed the structural steel nearing completion on the north end of the building. Tesla has said that facility is meant to eventually support production of up to 10 million units a year, though volume output there is not expected before 2027.

Commercial sales of Optimus are still targeted for the second half of 2027, but production is expected to start well before then. JPMorgan analyst Rajat Gupta has said Tesla’s “Optimus Academy” program, which uses early units to collect real world training data inside Tesla’s own facilities, is expected to be running later this year. Bloomberg Intelligence analyst Ian Ma described the Ningbo audits as “a positive commercialization signal for China’s humanoid supply chain,” noting that sentiment could improve further if the visit leads to confirmed supplier nominations and larger orders. The Solactive China Humanoid Robotics Index rose about 1.4% on the news, though it remains down roughly 30% for the year.

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Elon Musk

Tesla primes Cybercabs for 4K streaming and high bandwidth gaming with Starlink integration

Tesla is now shipping Cybercabs from Giga Texas with Starlink hardware built in as standard.

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tesla cybercab with no manual controls showing a movie with two employees inside

Tesla’s Cybercabs are now leaving Gigafactory Texas with Starlink hardware on the rear hatch in significant numbers, according to drone footage captured Tuesday by longtime Austin drone observer Joe Tegtmeyer. Production at the factory ramped back up after the Labor Day weekend, and his flyover of the outbound lot showed rows of gold Cybercabs alongside Model Y Long Wheelbase units, many carrying the satellite module for the first time as standard equipment rather than a one off retrofit.

Tesla first showed Starlink built into an actual Cybercab on August 10, when the Robotaxi account posted images of a single gold unit with the antenna integrated into the roofline above the taillights and called it the first Cybercab with Starlink integration. That followed a July reveal where Tesla and Starlink jointly posted a cutaway diagram of the antenna placement without a working vehicle to back it up. Ashok Elluswamy, Tesla’s VP of AI software, said at the time that the connection isn’t required for the car to drive itself. It exists mainly for navigation, customer service and keeping tabs on the fleet.

Musk has made a different case in public. During Tesla’s Q2 earnings call, he said the company can’t afford robotaxis stranded in what he called “Bermuda Triangles of lack of cellular connectivity,” and he separately claimed on X that Starlink will eventually reach every Tesla built, calling it the only way to deliver high bandwidth to billions of vehicles. He has also pitched the antenna as an entertainment upgrade, telling riders they would be able to stream 4K video or play games during a trip.

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The rollout has moved fast since. Robotaxi service opened to the public in Austin on September 3, and Cybercabs had already been spotted with Starlink hardware in Houston and near Miami International Airport in the weeks before Tuesday’s factory footage showed the module shipping at volume rather than on scattered test units. Whether the satellite link earns its keep is still an open question. Tesla’s unsupervised service currently runs in dense metro geofences in Texas and Florida, markets where cellular coverage is already strong, which is not where the rural dead zones Musk describes tend to show up.

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