I just got these battery warnings today. I went over 50K miles 2 days ago... very suspicious, like they waited until the battery warranty expired to start giving me error messages. Only about $110 for Tesla to replace with a mobile appointment scheduled, but it is 11 days away. Am I safe to drive the car, or should I buy a battery locally?
First and formost: YMMV.
My 2018 M3 had a fault, not 12V related, warranty handled, back in the day. The Service Center replaced the battery as part of the repair. That's not the biggie.
The more interesting story is my previous car, a 2010 Toyota Prius. In many ways, the hardware architecture of the Prius mirrors that of the Tesla: There's a traction battery that, full-on, runs the two electric motors in the thing, and a high voltage to low voltage DC-DC converter that charges the 12V battery that runs all the lights and computers in the car.
The failure modes in both the Prius and Tesla are very similar to each other: If the battery is failing, it typically drops its output voltage from the usual 12 - 12.3V or so down to below 11V. As the voltage degrades, various hunks of electronics looks at that too-low voltage and fails. Which means that one can have a perfectly healthy traction battery but, without 12V, one is going nowhere.
Thing is, speaking as a EE who was part of the buck-stops-here crowd of analyzing hardware failures, if you've had one ka-pop! of error messages already, it's highly likely you're going to have a second, a third, or maybe just One More and that'll be all she wrote. And
where that happens is likely to be in the middle of nowhere (tm). The phrase, "Are you feeling lucky, punk?" comes to mind.
On the one hand, it's just a blame 12V battery. On the other hand, it's not, quite. Most 12V car batteries are designed to be able to dump out a significant number of amps in order to crank the ICE in cold weather; neither Teslas nor Priuses do that. (The Priuse's traction battery uses one of the motors to turn over the ICE, and either of the motors on that car are 'way more powerful than the usual ICE starter motor.)
If memory serves, the Tesla's and Prius's batteries are both AGM (Absorbed Glass Mat). When my Prius's battery failed one day on a shopping trip, I had the SO bring some tools and jumper cables, got the battery up a bit, started the car, drove straight to an Advanced Auto store, and got a replacement off the shelves. They loaned the tools and I had the Prius's battery replaced in a trice; when I sold the car, two years ago, that battery was still in there.
Let's see, 50k miles: I'm going to guess and say you're got a 2019 M3 or something. Check Advanced Auto: $260 something for a Diehard.
So you can get one, but it's expensive.
The only other problem... Sometimes, it's not a dead battery, but a dead battery charging circuit. You might want to look at the error codes to make sure. If it is, then getting a new battery will fix things just long enough for
that battery to run down.
Good luck!
