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Original 12V battery @ 99k miles. Should I proactively replace?

Rockster

Active Member
Oct 22, 2013
3,014
4,692
McKinney, TX
Title says it all: Model S March 2015 build, currently at 99k miles and we are on our original 12V battery. I don't want the car to strand or inconvenience anyone with an unexpected 12V battery failure so I'm wondering if I should just proactively replace it now?

I know the car is supposed to warn of an impending 12V failure but I've also read that those warnings sometimes do not occur, so I'm hesitant to put my faith in a warning that may not happen.

Part 2 of the question is how should I go about replacing the battery? I see three options out there:
  • Make a service appointment and just pay Tesla to take care of it.
  • Replace it myself with a lead acid equivalent to what Tesla would use.
  • Replace it myself with a Li-ion 12V battery from ohmmu,com.
I'm perfectly comfortable with replacing it myself and the cost difference between those three options isn't a big deal. I just want to choose the best solution.

Opinions?
 

powaking

Member
Feb 1, 2018
438
270
Massachusetts
Not all batteries are the same. I just replaced my MIL battery in her 2009 Camry for the first time! She doesn't leave the city and never drives on the highway and the car only has 35,000 miles. Some last years and some last just enough to pass their initial warranty. Looks like OP got lucky.
 

sorka

Well-Known Member
Feb 28, 2015
8,281
6,246
Merced, CA
12v batts for me rarely go longer than 2 years for some reason

The reason is that your car pulls 60 to 70 watts sitting there which comes out of the 12 volt battery. 6 times a day, when the 12 volt battery is new, the main battery contactors close for a few minutes to charge up the 12 volt battery. Each discharge cycle is about half the capacity of the battery.

Lead acid batteries are not designed to be discharged constantly all day long. They like to be kept full or they start to degrade.
 

Rockster

Active Member
Oct 22, 2013
3,014
4,692
McKinney, TX
I also have a march 2015 build with the same mileage. My battery has been replaced TWICE in the same period. How on earth are you still on the original battery?


I have no idea. I’ve scheduled Tesla to replace it. They’re only charging $39 for the labor. It’s not worth the trouble to do it myself for that.
 

Rockster

Active Member
Oct 22, 2013
3,014
4,692
McKinney, TX
Chiming in here to provide an update. I scheduled an appointment for Tesla to replace the battery and a few days before the scheduled Ranger visit Tesla postponed the appointment for a week because the parts were unavailable. That new appointment was to be this Wednesday. This past weekend, however, my Model S died unexpectedly and had to be towed to the service center. The problem appears to be a failed 12V battery.

Sigh.

If only Tesla hadn't postponed the appointment last week we could have avoided the headache Saturday evening of dealing with having the car towed. We had to put dollies under the rear wheels and all of us (me, wife, two tow truck drivers) rotate the car 90 degrees so that they could get it up onto the flatbed.

Next time, when I get the desire to replace the 12V battery I'm just going to order one online and do it myself.
 
  • Informative
Reactions: ReddyLeaf

Rockster

Active Member
Oct 22, 2013
3,014
4,692
McKinney, TX
Update:

It wasn't my 12v battery, after all. It was my main pack that failed. That's quite surprising considering we received a replacement pack barely seven months ago.

Oh, and the service center told me that whenever they replace a pack they also replace the 12v battery at the same time because of the relationship between the HV pack and the 12v. This means that we received a 12v battery back in April with that replacement pack (even though it wasn't shown on the service invoice?!?), which makes this entire thread about me proactively replacing the 12v battery entirely unnecessary.
 

thecloud

As rhythm raced inside, the ship came alive
Nov 24, 2014
1,775
1,646
Sunnyvale, CA
It's definitely not an unnecessary thread. Seems important to know whether impending 12V failure on a Model S will actually give you some advance warning of the fact, or will just abruptly tell you to pull over and then leave you stranded. If the 12V in a Tesla can go from apparently fine to dead with no intermediate warning notifications, that really calls for proactive replacement.

I'm also on my original 12V battery (as far as I know!), and my car is 6 months older than yours. :eek:
 

Rockster

Active Member
Oct 22, 2013
3,014
4,692
McKinney, TX
It's definitely not an unnecessary thread. Seems important to know whether impending 12V failure on a Model S will actually give you some advance warning of the fact, or will just abruptly tell you to pull over and then leave you stranded. If the 12V in a Tesla can go from apparently fine to dead with no intermediate warning notifications, that really calls for proactive replacement.

I'm also on my original 12V battery (as far as I know!), and my car is 6 months older than yours. :eek:


But note that my problem turned out NOT to be the 12v battery but, rather, the main HV battery. And, if the SC is correct, they replaced my 12v battery as part of replacing my HV battery back in April. So, my original 12v lasted for 36 months and 91k miles and was still going strong with the HV battery died.
 

thecloud

As rhythm raced inside, the ship came alive
Nov 24, 2014
1,775
1,646
Sunnyvale, CA
But note that my problem turned out NOT to be the 12v battery but, rather, the main HV battery. And, if the SC is correct, they replaced my 12v battery as part of replacing my HV battery back in April. So, my original 12v lasted for 36 months and 91k miles and was still going strong with the HV battery died.
Right, so that means your experience didn't really answer your original question: namely, does the 12V battery need proactive replacement, and when it dies, is it going to be a sudden event with no warning that prevents the car from driving?

I wonder if the car can be jumped from the terminal that's behind the nosecone, using one of those portable li-ion jumpstart batteries?
 

Rockster

Active Member
Oct 22, 2013
3,014
4,692
McKinney, TX
Right, so that means your experience didn't really answer your original question: namely, does the 12V battery need proactive replacement, and when it dies, is it going to be a sudden event with no warning that prevents the car from driving?

I wonder if the car can be jumped from the terminal that's behind the nosecone, using one of those portable li-ion jumpstart batteries?


We were able to jump the car enough to put the car into tow mode, which definitely helped, but that was the extent of the benefit we gained by jumping the battery.
 

jerry33

(S85-3/2/13 traded in) X LR: F2611##-3/27/20
Supporting Member
Mar 8, 2012
20,010
24,737
Texas
Right, so that means your experience didn't really answer your original question: namely, does the 12V battery need proactive replacement, and when it dies, is it going to be a sudden event with no warning that prevents the car from driving?

I wonder if the car can be jumped from the terminal that's behind the nosecone, using one of those portable li-ion jumpstart batteries?
There is normally a warning when the 12V battery is weak. However, it does depend upon how the battery fails. In the VW, the 12V battery shorts out and can't even be jumped (had one of those events each year that I had the VW--never again).
Yes, you can get power to it with a jump-start battery. However, it's best if you can put a charger on it for a while to give a bit of reserve. I think, but don't know, that the 12V BMS won't attempt to charge if it thinks the battery is dead.
 

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