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Model 3 12v battery dead

smatthew

Active Member
Jun 9, 2018
1,293
2,244
CA Bay Area
Agree, but FWIW my wife's 2015 S70D gave the obligatory '12V battery needs service' warning, and I had time to conveniently have it replaced. In the case of my 2018 P3D+, the battery was fine with no warning messages, and then cooked and at 6V the next day. Precipitous failure, not gradual degradation.
Either Tesla's charging algorithm is messed up, or there's something wonky with these batteries, or detecting 12V battery failure is tough!
I doubt it's option 1. Tesla controls the 12V charging algorithm, and probably even has engineering approval from their battery supplier that it's appropriate. If that was the issue, Tesla would have updated the software
It might be option 2. If Tesla had received large batches of bad 12V batteries, they could have sued the supplier and everybody would have heard, and both companies stock prices would go down. Or, they act like adults and settle their differences in private....... it's a possibility.
Option 3 is most likely true. It's tough measuring the health of a 12V battery. Most existing models rely on measurements taken during the cold cranking process - a data point that a Tesla can never possess.
 

MexiCanuck

Member
May 7, 2019
494
498
Vancouver Island
LOVE TESLA but it shakes me a little when I use the car for 1000+ mile road trips knowing that I could be stuck literally in death valley without any kind of major warning, I was hoping to use this post so people can say what to look out for/warning signs
I would be unhappy too if that happened to me.

I have had a no-warning 12 V battery failure on both my Toyota Prius and on my Ford Ranger, and on each of my two Mazda B4000s. I was pretty unhappy those times too.

Battery failure is not something unique to Tesla.
 

neurocutie

Member
Dec 2, 2019
365
180
upstate ny
Every car, not just Tesla, is at risk of sudden failure of the 12V battery. Nothing unique about Tesla in this regard.
what is "unique" would seem to be:
1) 2 years!! Every ICE car I've ever owned (at least 10 cars), its 12V battery lasted at least 5 yrs. The last ICE 12V battery I replaced was 8 yrs old and I didn't really have to replace it then as it was just a little weak but still started the car fine.
2) sudden failure that leaves you stranded. I've always been able to jump start a dying ICE 12V battery and limp along for at least another week or so -- enough time to go to Autozone or wherever and get the thing replaced on my schedule.
 

JTesmod3

Member
Jul 20, 2018
252
287
Los angeles
I would be unhappy too if that happened to me.

I have had a no-warning 12 V battery failure on both my Toyota Prius and on my Ford Ranger, and on each of my two Mazda B4000s. I was pretty unhappy those times too.

Battery failure is not something unique to Tesla.

That's a little comforting:), overall I can't imagine getting another car, just hope they learn from this
 

Jmolloy3

Member
Mar 10, 2019
43
52
TX Hill Country
Agree, but FWIW my wife's 2015 S70D gave the obligatory '12V battery needs service' warning, and I had time to conveniently have it replaced. In the case of my 2018 P3D+, the battery was fine with no warning messages, and then cooked and at 6V the next day. Precipitous failure, not gradual degradation.
Just had my 2018 flatbedded off today. Spontaneous death of 12V, ironically, about 2 hrs after mobile tech fixed charge port. No warning...
 

kaffine

Member
Apr 1, 2016
292
277
Las Vegas
The first time it happened after I had used my phone to install a software update. I got up the next morning and the doors wouldn't open. I thought something went wrong with the software update used another car to go to work. When I got home I figured out it was just the battery so I used jumper cable to open the frunk. It was a Friday before a 3 day weekend, I called and asked if I brought the battery in if they would give me a new one and they agreed.

The second time I got a warning and ordered an aftermarket battery. I was using the car for a week before the battery came in. I went to swap it and found the negative cable was loose. I'm guessing it was left loose when I had the charger replaced a little bit before the warning came up. I already had the other battery so I swapped it out so I'm not sure if the battery was actually bad or if more likely it was the loose terminal that caused the issue.
 

Frank99

April 2018 Model 3 LR RWD, EAP, FSD
Apr 7, 2016
370
503
Arizona
Mine died a sudden death. Car drove fine in the morning, no alarms or warnings. Went out at lunch, and it was dead as a doornail. Fortunately I was at home, so I opened the frunk using the wires under the little disk in the front bumper, exposed the battery and attached a battery charger. Within a second of attaching the charger, the contactor went "Clunk!", the lights came on, and the car was driveable, but now I had warnings about the battery. Drove over to the SC, and they graciously installed a new battery for me under warranty.
 
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KenC

Active Member
Sep 4, 2018
3,861
3,573
Maine
Not sure if this will help anyone; but if you're far away from a service center, and can't wait for a Mobile Ranger, I saw my local Sam's Club had a sale on 51R flooded batteries until Mid-June.
IMG_0623.jpeg
 
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cybergates

Member
Feb 14, 2017
553
240
So Cal
12/2018 tesla model 3 - dead as a doornail suddenly in the driveway. Called Tesla roadside assistance they came in 30 minutes w a new battery and car was up and running. Great service, but you'd think the MCU should be able to give a little warning notice ahead of time?! We have a 6/2019 tesla - was the battery issue better on that car?

Oddly enough I have a 11/2016 Model S and the battery has never been changed as far as I know?!
 

starmanj

Member
Nov 15, 2018
11
17
Islamorada, FL
Yeah, but you have a 2018 car. Model 3's consumed higher amounts of power while "asleep" in the early days, leading to additional charge cycles being put on the 12V batteries, leading to their early demise. That was resolved late 2019.
Apparently not fixed in late 2019. My 12v battery died summer 2020, was replaced at service center, and died again yesterday parked in the garage. From the huge spate of reported 12v battery problems, I would say this is a bad quality issue with M3's...maybe limited to 2019 M3's, don't know.
 

smartypnz

Active Member
Supporting Member
Jan 23, 2013
2,227
2,437
Monterey Peninsula
2017 Model 3 in shop last week to upgrade computer. In their normal checks they discovered a 'weak' 12v battery and replaced under warranty. Just completed an 11.000 plus mile trip, so glad it waited. But, rule of thumb in my previous ICE days was 4 years plus a winter - replace no matter what. Of course that was for cooler climes
 

Dolemite

is my name
Sep 19, 2019
1,372
1,733
Seattle, WA
There is a series of videos by frugalteslaguy on you tube. The one talks about various replacements.



1625415122657.png


1625415153131.png
 

Matsayz

Active Member
Jul 6, 2019
1,195
973
Las Vegas
You can get it for $84 dropped of by a Ranger and do it yourself if you want to save afew bucks….10 minute job.

Ski
Oh that's good to know. I'll watch the install so I can do it on the wife's Y in a year or two. I just hate all the damn clips, broken so many doing the air filter change
 

android04

Member
Apr 1, 2016
517
527
Southeast Nebraska
So is the saga continuing,
or have all the bad batteries died and been replaced by now,
or should I keep a little $21 rechargeable battery and some duct tape and alligator clip leads (to open frunk and get to the nearest SC) in the car?
Get an A23 battery (https://www.amazon.com/Energizer-Mercury-Alkaline-Batteries-Packaging/dp/B00004YK10/) and put it in a Ziploc bag. Then roll it up and tuck it behind the tow hook cover. That will allow you to open the frunk if the 12v battery dies (and you can test it out by unlocking your car). Then you can carry a portable jump starter in the frunk or ask somebody to give you a jump start.
 

Fernand

Active Member
Mar 22, 2019
1,622
1,794
Northern california
Much appreciate the counsel. But once jump-started, can the car run if the 12v battery is dead ?
If that is true, then all the electronics can run off the main battery pack, right?

If the 12v battery powers electronics, then wouldn't it be better to jerry-rig in a 7-9 AH $20 lead acid battery that could (?) provide enough amperage to start up the electronics and accept a charge from the mothercircuits ?

Or is it known that much amperage is required for the car to drive and start ok?

I'm confused. Is it that normally the 12v battery is powering a lot of stuff but in parallel with a converter off the main battery, making it necessary only before the system is fully started? In that case what's minimum capacity required to get the car booted up, and would a small 7-9 AH battery be enough to get going out on the road if the real 12v battery fails?

Where can I find out what exactly normally runs exclusively off the 12v battery? Is there a diagram anywhere?
 
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