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When to Replace 12v?
- Thread starter everydaychris
- Start date
Place me also in the camp of believing the software that monitors the health of the 12V is horrid. I'm 0/3. First experience was my 2018 M3. At about 20-22 months of use, I suddenly began experiencing massive failure of varying systems. First noticed when the AC would not cool. Nav screen started throwing multiple error messages about different systems -- nothing about the 12V. Had to get to work; on the way home the brakes did not quit completely, but I had to use a greatly exaggerated amount of force on the pedal to get the same braking power. One message indicated only a single motor was running. And no lie as I came down my own street only a half block from my house, the freaking headlights went out. Pretty terrifying. I was deathly afraid it was some sort catastrophic failure so I was hugely relived to hear the service guy say it was likely a 12volt needing replacement. Mobile came and took care of it - under warranty. Never once got a 12V message. Tech was a good guy and when I described my experience he said "yeah, we prioritize the battery swaps."
2nd experience was wife's 2021 MY. Again, right at about 22 months -- brick. It was still under warranty and Tesla roadside sent a tow truck who brought it to the dealer, which given what I know now seems ridiculous but it didn't cost me anything so oh well. 12V was all it was. No message, no warning. I ragged on the guy I mean, c'mon, the thing can drive itself, has a full on computer that's doing all kinds of monitoring and calcs, basically the most sophisticated car on the road -- and it can't tell me to change the battery!
3rd time was the M3 again. No message, no warning, got in one morning to go to work, stepped on the brake to put it in Drive and -- boom, dead. Went to open the door and as it opened the door rolled down slightly like it normally does -- and that was it. Nada after that. By this time I've read up a little bit, and actually had a battery charger I bought for the battery on our home generator (required equipment in south florida). Was able to "jump" open the frunk and got to the battery, and just as the frunk opened, I got a push to my phone: "warning: change 12V battery." Thanks.
The charger/diagnostic said it could not be charged and indeed, it would not take a charge. Because you're supposed to disconnect the main battery when you swap the 12v and I didn't quite feel comfortable doing that, and you have to open both back doors which was another science project with no electric, I wound up punting and having it towed to the dealer, who recommended a "full diagnostic" to make sure it was nothing else. (Whatever.)
So I get there are folks out there 4 and 5 years on the same 12V -- but my experience has been dramatically different. And the Y experience was only about 6 months ago, so hard to believe there's been a lot of improvement in the warning system. And FWIW, on an ICE vehicle even a casually mechanically inclined person can recognize the signs of a dying battery, cranks slower, lights slightly less bright, etc. Low tech but better than bricking the thing.
So put me in the "proactive change" camp with apologies to Mother Earth and a plea to Tesla to step up their 12V game!
2nd experience was wife's 2021 MY. Again, right at about 22 months -- brick. It was still under warranty and Tesla roadside sent a tow truck who brought it to the dealer, which given what I know now seems ridiculous but it didn't cost me anything so oh well. 12V was all it was. No message, no warning. I ragged on the guy I mean, c'mon, the thing can drive itself, has a full on computer that's doing all kinds of monitoring and calcs, basically the most sophisticated car on the road -- and it can't tell me to change the battery!
3rd time was the M3 again. No message, no warning, got in one morning to go to work, stepped on the brake to put it in Drive and -- boom, dead. Went to open the door and as it opened the door rolled down slightly like it normally does -- and that was it. Nada after that. By this time I've read up a little bit, and actually had a battery charger I bought for the battery on our home generator (required equipment in south florida). Was able to "jump" open the frunk and got to the battery, and just as the frunk opened, I got a push to my phone: "warning: change 12V battery." Thanks.
The charger/diagnostic said it could not be charged and indeed, it would not take a charge. Because you're supposed to disconnect the main battery when you swap the 12v and I didn't quite feel comfortable doing that, and you have to open both back doors which was another science project with no electric, I wound up punting and having it towed to the dealer, who recommended a "full diagnostic" to make sure it was nothing else. (Whatever.)
So I get there are folks out there 4 and 5 years on the same 12V -- but my experience has been dramatically different. And the Y experience was only about 6 months ago, so hard to believe there's been a lot of improvement in the warning system. And FWIW, on an ICE vehicle even a casually mechanically inclined person can recognize the signs of a dying battery, cranks slower, lights slightly less bright, etc. Low tech but better than bricking the thing.
So put me in the "proactive change" camp with apologies to Mother Earth and a plea to Tesla to step up their 12V game!
Yeah, once you've been bricked, it kind of handles the curiosity factor for you lol
Then they will likely charge you. I replaced mine last month (3 years mark) and asked the SC to preemptively replace it. They said mine didn't have any battery warning message and will not be replaced for free under warranty.
JayPaul
Member
I bought a used from Tesla 2019 TM3 and 2021 TMY this year. I had both 12V batteries preemptively changed. The price of the Lead Acid battery is just too cheap to risk being stranded. I have a 2 year old that commutes with me to work (his daycare is at my job) I’m not going to get stranded with him, especially with NY winters. I keep A23 12v batteries in a cut rubber glove zip tied to the 12v jumper under the toe hook cover.
For the price, it’s totally worth it to change the 12V every 3-4 years.
I’d rather waste a little money, than have my son be uncomfortable, or worse, in danger just to save $125.
For the price, it’s totally worth it to change the 12V every 3-4 years.
I’d rather waste a little money, than have my son be uncomfortable, or worse, in danger just to save $125.
Farmer
Member
I always preemptively changed 12V batteries on my ICE cars beyond 4 years. I just didn't need that drama in some parking lot on a cold, rainy night, and they're fairly cheap. I usually did it myself on my terms and time, in good weather - old battery got recycled, no big deal.
whisperingshad
Active Member
my 2020 MY got trade in at the very end of last December and one reason was I want to have 12v L-ion battery. Interestingly, my 2017 Bolt EV still have the original 12v battery. As I leave the Bolt outside, few days ago I got Propulsion Power Reduce warning during -12 degree cold. Bolt owners have all kinds of speculations-one was 12v battery needing replacement. I went to Advance Auto, got checked and found the battery health is still very good.
My 12v battery died yesterday (Sunday) WITHOUT WARNING on my 2020 MYLR. Short version: my car was stuck outside, with the driver window partially open, and the car would NOT drive. With the rain in CA yesterday, it was a total nightmare. You absolutely can get stranded if the 12v battery dies.
Here's the full story on another thread: 12v question
Here's the full story on another thread: 12v question
For me, it’s a tiny inconvenience for $130 and like 30 minutes of my time to have the peace of mind every three years with a new battery. And not worrying that my wife will be stranded.
My MY is 3.75 years old, (68K miles) and I walked into the Smithtown, NY service center last week, where the underwriter told me that there was no reason to change the 12v battery in the absence of error messages on the screen. I scheduled it anyway (along with electively scheduling the HEPA mod and upgrading the repeater cameras on both sides) and doing it all will reportedly by $850.00, tax included. It’s scheduled for tomorrow morning. This is the only maintenance I have put into my vehicle in the past 12 months, and I feel that in doing so I am optimizing safety and reducing the likelihood of getting stranded.
JayPaul
Member
I was told the same, did it anyways like you are planning.
You have a Y with the repeater cameras with the LED light bleed? I had that on my 2019 TM3, but my 2021 TMY doesn't have that problem. I upgraded the repeaters on the TM3 very soon after getting it, since I drive when it is mostly dark.
I did the Biodefense mode added to my 2021 TMY a month ago (it was early 2021, before biodefense mode was added).
@ArtK, @JayPaul, we're already acquainted here. You should be glad you replaced/are replacing the 12v battery before it's too late. The number of errors I got when the 12v battery died was stupid. I took screenshots when they occurred and you can see them here: 12v question
I think one thing that really hurts EVs with the 12v battery issue is that ICE cars tend to give you some indication that the battery is failing. You know, generally, that it’s taking a little longer to turn over than usual, that something isn’t working exactly right. Now, that’s not all the time, but most of the situations where I’ve had a battery fail it was fairly obvious that it was failing for at least a few days before it did (sometimes more like a month or more, I just didn’t do anything about it). EVs don’t give you that same level of indication, there is no “oh, the lights dimmed really weird there when I started the car,” or “oh hmm, starter usually only goes for a split second, that’s not right” moment to see.
JayPaul
Member
This is true, but has become less and less true. Even ICE vehicles have tons of computer systems these days. When they go, they can immediately go. The difference with EVs (I only have experience with Teslas) is it seems we can’t just easily jump and keep driving.
Tesla should find a way to use the HV battery in place of the 12v battery once it dies. Then let the driver that the 12v battery needs to be replaced.
Fair point about it being less true. And temperature changes can have a pretty dramatic impact too. A battery that will start just fine when it’s 75F might not when it’s 15F!
Johnny Vector
Member
For safety reasons (and probably regulatory too), the HV battery has to be isolated when the car is "off". Which means you need a power source to run whatever mechanism connects it to the rest of the system (a high-current switch of one type or another).
OTOH, it's not like there's no circuitry on the battery side of the HV switch; all the battery management system is there. So maybe you could find a mechanical or optical way to communicate to the HV side that you want to close the main switch, and it could do it using its own power. You'd have to think about the safety implications, but it might be possible.
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