Tesla Support, Low 12V Battery Issues, Home Charging settings

Tesla Support, Low 12V Battery Issues, Home Charging settings

Just had my first customer support call into Tesla.

A red warning indicator on the Center Console told me to call Tesla Service.

I call the support center and after being routed several times had to leave a voicemail. I got a call back 10 minutes later. I gave the service rep my VIN so they could check on the vehicle remotely. The service rep told me the issue was that the 12V battery had run low. The car should have autonomic systems that detect and address the low charge, but for now, the remedy was to manually initiate a charge cycle, even though I was at 90% of my standard charge.

Interestingly, the service rep also had me lower the 40amp max amp setting to 12amps so the charge cycle could get drawn out more. I asked how this helped the 12V battery and the service rep said that longer charge cycles are better for both the 12V battery and the main battery. In general, he recommended that I reduce the 40amp max setting for my 14-50 outlet charger to 25 or 30 amps so that I can draw out the charging when I charge overnight. Then he said that the fast charging at superchargers was detrimental to the battery.

I don't see how the slower charge cycle hurts me as I have plenty of time to get to standard range overnight. However, I'd like to know if any other owners have been given this same advice and can help me understand if slower/faster charging affects battery health. Also, has anyone else had issues with a low 12V battery? any idea what conditions cause the 12V battery to go too low and why the car sometimes may not be able to address this on its own?

StefanT | April 27, 2013

I got a call this week from Tesla service that said they had been reviewing data from my car and the 12V battery needs replacing and the firmware that controls charging of the 12V battery needs updating. I had no indication from the car there was any issue. The ranger is coming next Friday to perform the maintenance. Incidentally I have only been charging the car with 110V since I got it in mid-Feb so I have pretty much the longest charge cycle possible.

It would be helpful if people would indicate either a build date or VIN when stating technical issues so we would have some context.

ichong | April 27, 2013

@StefanT I got my car in March

shop | April 27, 2013

There is a very long thread over at TMC about this. @ichong, presumably they are going to physically repair something as well? How long have you had the car?

mark_g | April 27, 2013

The 12 volt battery is charged using trickle current during a charge cycle (there is no connection between the 12v and 400v battery). The longer the charge cycle the more trickle current and thus the more charge to the 12 v. Shorter charge cycles result in less charging current to the 12v battery and thus more likely to discharge. I do the same thing occasionally by charging with my current limit at 5A.

Robert22 | April 27, 2013

It's always been intuitive that slower charging might be beneficial for the battery but I think Tesla has now stated that supercharging and fast charging with the HPWC has no detectable deleterious effect on battery longevity. Apparently they've been supercharging a car through numerous cycles for some time now with no indication of battery degradation. It's surprising to me that a rep gave you that information, however, my info may be outdated unless they are speaking specifically about the 12 volt battery alone. I'm sure others can speak more authoritatively to this issue.

P.S. The car is indeed evolving quickly but I don't think it has a nervous system yet (autonomic) ;)

FLsportscarenth... | April 27, 2013


Cylon car? hehe

akikiki | April 27, 2013

We've seen several cars, with 12V battery issues. The batteries are being replaced by Tesla. Mine has been replaced. I car could not perform the firmware update even though the main battery was fully charged. I don't consider the 12v battery as an issue. Sometimes there's just a bad batch of parts and they make it to production cars. This has always been a common occurence in ICS for many years. I used to work for a dealership and saw it often. In the case with the MS, its not a lot of cars. But Tesla is on top of it monitoring the cars before most of them become a serious issue.

negarholger | April 28, 2013

There is a physical connection between the large battery and the 12 V battery and it is called the DC-to-DC converter.
During my last visit service they updated the Dc-to-DC converter firmware.
Problem is that the 12 V battery controls the main battery switch. If the 12 V battery is dead then the whole car is dead and can not be recharged from the main battery. Watch the emergency instruction video - nicely explained there.

jat | April 28, 2013

I don't know exactly how closely this applies to the Model S batteries, but in general Lithium batteries have no issue at all with being charged or discharged below the 1C rate. For a 85kWh battery, the 1C rate would be 85kW. Even HPWC charging at 80A is only about .24C, so that is no issue at all. Supercharging at 90kW is slightly above 1C, but that still shouldn't be an issue.

Brian H | April 28, 2013

I've seen statements that up to 4C is normal, tolerable.

deenie | July 14, 2013

i have a 6 day old S, and this morning it was dead. Service call seems to indicate the 12V battery. Seems like the problem is not solved.

Robert22 | July 14, 2013

According to those reporting from the Teslive event, Tesla will soon be pushing notifications to the screens of those cars believed to possess a battery likely to punk out prematurely.

eshih02 | August 12, 2013

Yes, I got service warning light this morning that my 12V was low with the dire warning that car may turn off unexpectedly and pull over immediately.

Fortunately car was in garage, but I'm waiting for the service center to call back.

loud | January 14, 2014

With my Model S I got the low 12V battery message and Car may not restart message. Now when I attempt to plug in the cord for charging, it does not seem to want to connect the charger. The light remains light blue i color. Initially it would go to green then switch to red, but now it never get to red or green.

I am scheduled for a ranger visit this Thursday 1/16. I wonder if this is also the firmware issue as well as the 12v battery issue.

Any comments would be helpful because it is a 2.5 hour drive one way for the Ranger.

TeslaMom | January 14, 2014

@loud did service advise you to connect to a 120v outlet to charge the 12v battery? I had the same symptoms just before the holidays. Not a battery issue but had poor connection from the main battery due to a failed seal. Doug in Columbus took care of it within a day.

Brian H | January 14, 2014

A trickle-charger hooked to the posts under the nose cone?

TeslaMom | January 15, 2014

Just plug the UMC into a 120v outlet. If that doesn't work you'll have to pull the nosecone if you want to connect the trickle charger.

riceuguy | January 15, 2014

It sounds like either way you should have the ranger come out!

brian | August 23, 2015

Yep, just got the message and mine is 60 days new a year and a half after the last message here. Really? Top of the line $120k car and I now have to figure out how to charge or replace the 12V battery?

How about if Tesla service calls me and comes and picks up the car to fix this. This is supposed to be a low maintenance car.

P.Dolby | August 23, 2015

This should have been solved long ago. It's a shame that we are still seeing this crop up. The car is nothing BUT battery. I get why it needs a 12V system.. but dang. This seems eminently solvable.

Perhaps some kind of battery eliminator circuit that does a 12V pick off the main battery.

prp | August 24, 2015

@p.dolby, given the higher failure rate of the 12v battery, do you really want that as part of your main pack?

mallynb | August 24, 2015

Closest SC, 170 miles away, scheduled a Ranger visit for the Monday following a 12V battery warning received on a Friday afternoon. Continued driving over the weekend wasn't a concern to SC. Original battery was replaced on Monday. Model S was almost 2 yrs old.

P.Dolby | August 24, 2015

Perhaps I was unclear... I don't think there should BE a 12v battery. Just a voltage converse to pick off 12v to run the anslary equipment.
I'm sure they thought of this and there is a reason we don't know about that makes the 12v battery a necessity.. But they should have figured out optimal charging for it by now.

The only issue I could see with a BEC is fusing for main fuss box power.

WØQR | August 24, 2015

mferrazano: this doesn't seem right to me. I think you would continuously have to charge the 12volt AGM battery or it would go dead all the time. It is only 30Amp Hours. I think it is cycled even when not plugged in by grabbing power from the Lion battery pack. I'm going to monitor this and see if it is true. Should be able to measure the voltage of that battery at the 12v ACC socket. Anyone else have an insight into this?

murphyS90D | August 24, 2015

You can't do it at the 12 volt socket. That turns off when the car shuts down. You can do it at the battery terminals behind the nose cone. I have observed the 12 volt battery being recharged up to 5 times a day. It is an AGM battery and they have a number of recharges limit. When the number of charges limit is exceeded it's time to replace the battery. Here is a link to a picture in my dropbox that shows the battery voltage over a 24 hour period. The car was not plugged in. Note the steep discharge slope. I've misplaced the sample rate but it looks like it is 10 times per minute.