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Any chance we can get a sticky thread for the 12V battery?

I've got a 11/13 built S85 with the MCU2 upgrade and have finally had the "12V battery low" message pop up after 112K miles. Tesla has preemptively replaced the 12V battery twice before, one when the HV contactors were replaced under warranty and the other time rear window defroster was fixed under warranty. I plugged in my Anker battery monitor into the 12V socket over the last week and saw the voltage fluctuate between 12.7-13.4V. I sent in a request via mobile app for Tesla to remotely reset the battery warning because I'm not convinced it needs to be replaced. Instead of doing that, Tesla set up mobile service to replace the battery for ~$265 ($159 for the battery, $89 labor, plus tax). I've searched threads to learn what I could about the 12V battery and thought instead of having threads about the 12V pop-up every now and again that perhaps there should a be a sticky with how the Tesla Model S uses the 12V battery, how it charges, and how to prolong the life. Personally, I'm surprised Tesla hasn't engineered their own auxiliary battery system that to be better than the traditional system.

BTW, does anyone know the threshold voltage that the Tesla needs to power and start the car? I believe 10.8V was necessary for both my old 2007 Lexus Rx400h and our 2013 Fiat 500e. Our S typically sits for days on end in our garage and with the MCU2 and newer software I've noticed that the pumps run and the contactors audibly open and close at least a few times a day. In hindsight, I regret not placing a 2A trickle charger on the battery posts (behind the nose cone) as that could have prolonged the life of the 12V...it's about 2.4 yrs old at this point. We've gotten more than 6 yrs out of the tiny battery in the 500e, but that car does not have all the connectivity and vampire drain that the Tesla come to know.
 
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the 12v battery isn't like a normal car battery it is a deep cycle battery and has a different point at which it fails. if you get the replace 12v warning just go buy the battery from tesla and replace it in your driveway its not rocket surgery its a 10-20 min job.
Pull out the frunk liner (2 bolts and 2 nuts) then the 12v is right there in plain view. Unless you have the old old location in which its by the passenger wheel well in which case its like an extra 5-10 min job but again still super easy.

You can go to fixyourtesla.com to see the instructions on how to do it but since that site has been taken down you need to use the wayback machine and find one from early last year. its blocked on my work computer after i post this i will edit it with a link from my phone.


 
I got tired of seeing the low 12V battery warning when I'm consistently getting 12.8V in the morning so I did the ole hard reboot by changing the wheel configuration under the "Service" menu on the MCU. Annoying message gone but I'll keep an eye on the battery health. I'd love to know the minimum voltage needed to start the car. Upon researching the 12V battery, it seems like Tesla has had issues with them dating back to 2014 and I'm not sure if they ever came up with a remedy.
 

Tevvy

Member
Jul 6, 2017
287
129
UK
I've got a 2017 MS 75D and have had the 12v battery warning on for over a year now. There's nothing wrong with it at all, I monitor the voltage on a monthly basis and it's always over 12.4v.

I occassionally do the 'wheel configuration' reset and this clears the warning for a while (maybe a couple of days) but it always comes back. I asked a mobile technician why it keeps coming back and he said the battery has some kind of 'trip switch' in it, which means if it ever shows a low voltage or anything like that, then it's ALWAYS going to error and the only thing to do is replace it. Very poor from Tesla,
 

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