Surprised at how little info on 12V battery there is out there - so sharing my recent experience. Just another day until went out to the M3 (12/18 delivery) and heard loud noise from frunk, didn't think much about as have heard similar when charging, but on entry to the car the windows barely moved down and behaved as if "battery" dying. Then got a steady procession of error messages about this not working that not working, etc. Real nightmare. Thought WTF, and just exited, let it sleep, then came back in. At that point all I had was the replace 12V battery soon message. Eureka I thought, no big deal. Seemed to behave fine, then on driving I noticed the fan for the AC would not blow. In October in Miami that's a big deal.
Went through the service app and got an appointment for like 6 weeks out. No es bueno. Beat my head against voice mail jail prompts trying to get to my local service center. While I was on extended hold, Tesla service via the app had rescheduled me for only 5 days out which I thought was great, but still longer than I wanted with no AC. Hoping to fenagle my way into a "quick 12 volt swap" at the dealer I hung in there, and eventually got a service person who told me he wasn't sure if the fan was related to the 12 volt issue or not, but "don't worry about it because when you see the light you still have a long time before the battery actually goes."
The next day, my AC fan began blowing again. Meanwhile, I was doing a lot googling and found videos on how to swap the 12V out but not really anything on symptoms. Over the next 4 days, I had major failures to include headlights and brakes, and little stuff like the windows not aligning correctly. Favorites were on way home from work pulling down my streets and "click" the headlights went out. Poof! Running lights stayed on, but no fun. Next night in parking garage at work put foot on brake to wake car and immediately felt stiff resistance and brakes basically required huge amount of pressure to get to a full stop - thank God for regen braking.
At this point I didn't know if I was just having a series of catastrophic computer issues or if the 12V was crazy important focal point of the vehicle, and the service guy was (forgive me) a complete idiot. The mobile guy showed (raining!) and quickly assured me that everything I had been experiencing was not unusual, and that when you see a 12V light you should get the battery replaced right away, and that the mobile service prioritizes those calls to the "top" of their list. He actually asked me if I got a name from the service center because he was ready to "call and ream him a new one" - I appreciated the passion and attention to customer safety. BTW, he said 18-24 months is the average life span and added "so you're right on schedule." He also added that every time you wake the car even if you don't even get in it, you're cycling the 12Volt which is why they go so quick. (BTW, mine was $0 under warranty.)
In summary, when you get a 12V warning:
Went through the service app and got an appointment for like 6 weeks out. No es bueno. Beat my head against voice mail jail prompts trying to get to my local service center. While I was on extended hold, Tesla service via the app had rescheduled me for only 5 days out which I thought was great, but still longer than I wanted with no AC. Hoping to fenagle my way into a "quick 12 volt swap" at the dealer I hung in there, and eventually got a service person who told me he wasn't sure if the fan was related to the 12 volt issue or not, but "don't worry about it because when you see the light you still have a long time before the battery actually goes."
The next day, my AC fan began blowing again. Meanwhile, I was doing a lot googling and found videos on how to swap the 12V out but not really anything on symptoms. Over the next 4 days, I had major failures to include headlights and brakes, and little stuff like the windows not aligning correctly. Favorites were on way home from work pulling down my streets and "click" the headlights went out. Poof! Running lights stayed on, but no fun. Next night in parking garage at work put foot on brake to wake car and immediately felt stiff resistance and brakes basically required huge amount of pressure to get to a full stop - thank God for regen braking.
At this point I didn't know if I was just having a series of catastrophic computer issues or if the 12V was crazy important focal point of the vehicle, and the service guy was (forgive me) a complete idiot. The mobile guy showed (raining!) and quickly assured me that everything I had been experiencing was not unusual, and that when you see a 12V light you should get the battery replaced right away, and that the mobile service prioritizes those calls to the "top" of their list. He actually asked me if I got a name from the service center because he was ready to "call and ream him a new one" - I appreciated the passion and attention to customer safety. BTW, he said 18-24 months is the average life span and added "so you're right on schedule." He also added that every time you wake the car even if you don't even get in it, you're cycling the 12Volt which is why they go so quick. (BTW, mine was $0 under warranty.)
In summary, when you get a 12V warning:
- Get it fixed as fast as you possibly can
- Know that really any symptom may pop up spontaneously to include really serious safety issues
- Window issues are the most common (if you have one, make sure they re-calibrate when swapping battery)
- Per mobile tech, all this is pretty much the same for the S, the X and the 3.