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12V Battery Replacement Options

Techguy817

Member
Mar 14, 2015
29
5
Boynton Beach, Fl
Hi all!

Tesla remote diagnostic said that the 12V battery in my 2015 MS with 110K+ miles is reporting lower voltages than it should. No notices in my instrument cluster but they suggested I still proactively replace the battery (which has never been replaced). Mobile service is about $225 they said for parts and labor.

Trying to decide if I should just replace the battery myself, and if so, should I use a lead/acid one or a lithium battery (lithiums seem about twice as expensive but are lighter and supposedly last longer). I've done a fair amount of work on my car so far including replacing door handles, touchscreen MCU issue, etc. so comfortable working on it.

Welcome thoughts, suggestions, experiences, etc.

Thanks!
 

ADEEL421

Member
Sep 14, 2020
131
82
west palm beach
This sounds normal. battery normally last 3-5 years and then starts to fail. they show sign of low voltage and one day just fail on you leaving you stranded #personel experience! Definitely get it replaced.

I am assuming you are out of warranty so honestly by replacing it yourself you wont save ALOT. maybe a 100 bucks (guessing) or so but then add in to your consideration of your efforts and time. Now the main thing yo may want to ask Tesla is what is the warranty on the battery they will sell you? is it 3years? 5 years? no question asked? or prorated??
if they do then i would go with them for the peace of mind.

Normally off the shelf batteries you buy comes with some kind of warranty 3-5 years free exchange replacement. those come in handy if your battery fail pre-maturely. It's an easy swap if you have your receipt.
If tesla is not offering any warranty than i would go with one of these options. Just make sure to match the rating on current battery to the new one. Some reminders: Make sure the polarity terminal orientation is same (very important). Verify positive and negative terminals before final connections!
 

Doanster1

Member
Feb 14, 2018
955
492
Oregon
The concern these days is that there have been reports of different versions of batteries needing to be coded to the car, i.e. f/w flash is needed. There have been some threads about it recently. For $225, I’d def let a Ranger do it.
 

Techguy817

Member
Mar 14, 2015
29
5
Boynton Beach, Fl
Wow didn't realize something like the 12V might need firmware flashing. Curious how that might be the case? Is the power system monitoring current delivery characteristics in some manner?

Yeah for $225 I'm leaning towards letting the mobile techs do it for me. Even though it's a lead-acid battery and not as good as lithium, if it lasts me another 3-5 years or so I'll be happy. Plan to keep the car for a while though... ;)
 

Doanster1

Member
Feb 14, 2018
955
492
Oregon
That’s the weird part. New post in the other battery thread says Ranger just installed the battery and left. No update needed. maybe Ranger new which specific battery was needed for the specific car.
Other posts mention SC said there is a matched pair scenario. I wish it was conclusive because it shouldn’t be a PITA to just replace a 12V battery.
 

Rockster

Active Member
Oct 22, 2013
3,010
4,614
McKinney, TX
In October I:
  • Pulled the dash apart and removed my MCU1.
  • Opened the MCU, extracted the Terga board, and mailed the board off to be rebuilt.
  • Reinstalled the MCU (while waiting for the Terga board to come back) so that the car would still function, albeit without any intelligent functions.
  • Removed the MCU when the Terga board arrived, opened the MCU, installed the Terga board, reassembled the MCU.
  • Reinstalled the MCU in the car.
  • Discovered that I had not fully connected one of the ribbon cables in the MCU and the screen was not responding to touch.
  • Removed the MCU again. Opened it up, secured the ribbon cable.
  • Reinstalled the MCU.
  • Reassembled the dashboard.
Later in October, I also replaced the 12V battery myself. It was absolute hell.

I would much rather repeat the ENTIRE MCU effort outlined above than replace the 12V battery in my S again. No lie. Replacing the 12V battery on my particular version of Model S, where the battery is up against the firewall on the passenger side, was that annoying.

If this is where your battery is, I suggest you pay the Ranger to do it.
 
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Rider668

Member
Oct 29, 2018
18
22
Birmingham
Just had mine done - it’s easy (20mins) with an AWD 2015 car, and much harder with a RWD car which has the battery buried much further back according to the mobile tech who did it.
It only cost around £50 to get it done at my own home while I was working, and I was ok with that (even though this is the first time I have ever paid anyone to fit a battery!) because there was software involved in my case according to the tech. While he was doing it he also fixed a software problem with my charge port which was not always opening, without being asked because he could see the issue in the logs - who knew?
I’m with Rockster - just get on the app and let Tesla do it.
 
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Pluto

is a Planet
Nov 17, 2015
404
674
Auburn, AL
Thank you guys for sharing your experiences, I'm in a similar boat to the OP with a 5.5 year old and 103k mile Model S, and I've been putting off this first battery replacement for weeks after the the service message popped up. Interestingly the message says something like "updates will be held back" as motivation to replace the battery, which doesn't apply to me since working from home at an apartment full time where my car can't get close enough to WiFi to update in the first place. I was hoping to save about $100 in service, but it seems like this isn't the place to do it.
 

davidc18

Active Member
Apr 25, 2015
1,828
1,235
Ft. Lauderdale
My 12V died suddenly, luckily in the garage. Called Tesla SC, had battery in stock. I think 162 dollars and 30 minutes to swap the batteries and I was back in business.
 

HenryT

Member
Jan 29, 2020
578
468
Manchester
Just had mine done - it’s easy (20mins) with an AWD 2015 car, and much harder with a RWD car which has the battery buried much further back according to the mobile tech who did it.
It only cost around £50 to get it done at my own home while I was working, and I was ok with that (even though this is the first time I have ever paid anyone to fit a battery!) because there was software involved in my case according to the tech. While he was doing it he also fixed a software problem with my charge port which was not always opening, without being asked because he could see the issue in the logs - who knew?
I’m with Rockster - just get on the app and let Tesla do it.

As a fellow AWD 2015 MS owner I am expecting to go down this route at some point soon - did you get much notice or any warning of impending failure, or was it just sudden death?

Also, what was the total cost, assuming you were outside warranty terms?
 

BrokerDon

Active Member
Aug 23, 2014
1,399
1,289
Newport Coast, CA
I had my 2015 P85D's 12V battery replaced a couple of months ago at my home by a Tesla Ranger. Worth every penny since they come to me, provide the correct battery, and know what they're doing. My time and avoiding liability not worth doing it myself even though I have the tools and experience replacing 2 HEAVY "golf cart" batteries in our Winnebago View RV + 1 HEAVY chassis H8 AGM battery in our turbodiesel Mercedes Sprinter RV.
 

Rider668

Member
Oct 29, 2018
18
22
Birmingham
As a fellow AWD 2015 MS owner I am expecting to go down this route at some point soon - did you get much notice or any warning of impending failure, or was it just sudden death?

Also, what was the total cost, assuming you were outside warranty terms?

Hi I got the standard warning from the car and I booked to get it changed and got an appointment in 4 weeks time. After 3 weeks the message disappeared, but I asked Tesla (via the app) to check the logs and they said the battery (which was 5 years old) was on the edge of throwing up another warning so I might as well change it - which I did. I guess the battery would have done a few more months. So plenty of warning.

The total cost was £197.20 fitted, all done on my drive and I was very impressed with the service. This was my second go with Ranger service - I got the CCS Combo 2 adapter done recently too. The Rangers here have Model S P90Ds with the back seats removed and tool drawers fitted. Very neat. Both rangers were very knowledgeable as they drive the cars as well as fixing them,
 

HenryT

Member
Jan 29, 2020
578
468
Manchester
Hi I got the standard warning from the car and I booked to get it changed and got an appointment in 4 weeks time. After 3 weeks the message disappeared, but I asked Tesla (via the app) to check the logs and they said the battery (which was 5 years old) was on the edge of throwing up another warning so I might as well change it - which I did. I guess the battery would have done a few more months. So plenty of warning.

The total cost was £197.20 fitted, all done on my drive and I was very impressed with the service. This was my second go with Ranger service - I got the CCS Combo 2 adapter done recently too. The Rangers here have Model S P90Ds with the back seats removed and tool drawers fitted. Very neat. Both rangers were very knowledgeable as they drive the cars as well as fixing them,

Glad to hear you had some warning about the failing battery - thanks for the clarification.

As it happens, I've had the CCS update too and also found the ranger service very good so wouldn't hesitate to use them again.
 

galvatron

Member
Mar 15, 2020
120
75
WA
As a side question on this topic, does anyone know how the 12V battery gets recharged by the Model S EV battery? I know in a gas car, if I leave my car sitting over the winter months, I put a battery tender on my battery. On the Model S, as long as I keep the EV battery charged, does that mean my 12V battery will automatically be charged too, even if the car is sitting unused all winter? Or do I actually have to have the car ON before the 12V gets charged by the EV battery? Any idea how that works? Do I need a battery tender for the Model S 12V battery also?
 

HenryT

Member
Jan 29, 2020
578
468
Manchester
As a side question on this topic, does anyone know how the 12V battery gets recharged by the Model S EV battery? I know in a gas car, if I leave my car sitting over the winter months, I put a battery tender on my battery. On the Model S, as long as I keep the EV battery charged, does that mean my 12V battery will automatically be charged too, even if the car is sitting unused all winter? Or do I actually have to have the car ON before the 12V gets charged by the EV battery? Any idea how that works? Do I need a battery tender for the Model S 12V battery also?

Pretty sure the 'big battery' takes care of the 'little battery' which I assume contributes to the vampire drain to an extent. I'm sure others will be along with a more accurate explanation, but I think that's the general idea.
 
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maximizese

Member
Jan 16, 2018
474
453
California
As a side question on this topic, does anyone know how the 12V battery gets recharged by the Model S EV battery? I know in a gas car, if I leave my car sitting over the winter months, I put a battery tender on my battery. On the Model S, as long as I keep the EV battery charged, does that mean my 12V battery will automatically be charged too, even if the car is sitting unused all winter? Or do I actually have to have the car ON before the 12V gets charged by the EV battery? Any idea how that works? Do I need a battery tender for the Model S 12V battery also?

I had my 12V battery replaced gratis from my Service Center when they replaced the HV contactors, HVAC drain hose, and drive unit, all under warranty. I was still getting 12.6V reading out from my Anker ROAV battery monitor, but I think that must be standard protocol to replace the battery when the contactors are bad.

As for the 12V battery recharging, I believe the HV battery connects with the 12V battery when you open the driver side door (you'll hear a double-click or pop noise) to recharge the battery. Conventional ICE vehicles use a belt to turn an alternator to recharge the 12V battery; EVs and hybrids use a DC-DC converter.

Our 2007 Lexus Rx400h would go through 12V batteries pretty much every 37 months (on a 3-year free replacement battery). The window and steering wheel tilt motors would slow down and interior lights were dim a bit about a week before the car would no longer "Ready." It would "Ready" at 11.2V but no longer at 10.8V.

I know our 2013 Fiat 500e had a recall for a software patch to fix an issue that would drain the HV battery when you left a 12V accessory plugged in with the car off. I assume this left the contactors open and the 12V accessory would potentially drain the HV battery if left on low SOC% for days.

Definitely a lot to learn about the new way cars work and how they're programmed.
 

Evoforce

Active Member
Apr 19, 2017
1,511
1,785
Fountain Hills AZ
Hi all!

Tesla remote diagnostic said that the 12V battery in my 2015 MS with 110K+ miles is reporting lower voltages than it should. No notices in my instrument cluster but they suggested I still proactively replace the battery (which has never been replaced). Mobile service is about $225 they said for parts and labor.

Trying to decide if I should just replace the battery myself, and if so, should I use a lead/acid one or a lithium battery (lithiums seem about twice as expensive but are lighter and supposedly last longer). I've done a fair amount of work on my car so far including replacing door handles, touchscreen MCU issue, etc. so comfortable working on it.

Welcome thoughts, suggestions, experiences, etc.

Thanks!
I have been using an Ohmmu battery for 3 and a half years in my model S. Actually it was called Battmobile when I purchased it. It has worked well and actually did not need reprogramming for my car. The battery also has a BMS to protect itself against over discharge should your main traction battery contactor not energize because of a faulty HV component or other fault drain.

It has saved me from having to replace the 12 volt when my traction motor developed a bad seal and shorted. Your 12 volt battery will get drained very rapidly when it is not getting a charge through the DC-DC because of a HV fault. Unlike a lead acid, it will protect itself whereas a lead acid will completely drain. A lead acid cannot be trusted (especially on a Tesla) once it has been completely discharged. That is why many times a Tesla breakdown also gets a new replacement 12 volt. With an Ohmmu battery, you would not need a replacement even if your broken car sat for days waiting for repairs. A lead acid would be hammered...
 

Pluto

is a Planet
Nov 17, 2015
404
674
Auburn, AL
Cost in California for mobile service was $258 for parts, labor and tax:
upload_2020-11-24_10-30-19.png
 

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