12 Volt Battery Issues

12 Volt Battery Issues

I have an 85D that is 4 months old and 15K miles. On my way home from work i got warnings that my car needs service and "may" shut down.
By the time I got home my car completely died. Looks like the 12 volt battery is already dead. I read about this in older posts but thought these issues were resolved? Anyone else still having issues or am I the only lucky one......

J.T. | 22. november 2015

They usually check the 12v at the 12,500 mile service. What happened at yours?

jbowers | 22. november 2015

Everything checked out great! Had service two weeks ago. Talked to service department on my way home tonight and they ran some diagnostics and didn't see a problem with battery. it's dead now..... tow company will have fun getting it out of my narrow garage....

jbowers | 22. november 2015

When i first contacted service today reporting the error "Car needs service - may not restart" this was their response:

"We reviewed the logs and currently do not see anything abnormal. We believe it is a one-time occurrence. If you experience any further issues let us know."

Unfortunately, an hour later my car was dead :(

Hopefully something easy to fix.......

Bighorn | 22. november 2015

May well be the contactor, though you'd presumably have one of the latest iterations.

Anthony J. Parisio | 23. november 2015

Please keep us informed. I hope it's resolved quickly.

digiprime | 23. november 2015

Hi, Sorry for your problem. I hope it will be solved soon.

I'm wondering though... Do you plug in your car all the time when it is parked in your garage, or only when you charge it?

vlad22 | 23. november 2015

I would bet on a contactor failure. I think the 12 volt battery problems have been mainly solved. Tesla will get you looked after. Hope everything goes smooth for you.

jbowers | 23. november 2015

I'm probably plugged in 60-70% time. I even charge at work during the day. Sometimes if I have over 200 miles remaining I won't charge at night. I drive over 3K per month so I see a lot of superchargers as well....

jordanrichard | 23. november 2015

At this point I believe the issue isn't the batteries but something about the driving/charging of these new individual cases. I took delivery in Mar. 2014 and 36,000 miles later, still no issue with the battery. 99.9% of the time, I plug my car in regardless of the SOC.

AmpedRealtor | 23. november 2015

Whether or not you keep your car plugged-in should not cause any issues with the 12v. If the 12v needs a charge, it will get it from the main pack.

Pungoteague_Dave | 23. november 2015

The issue on the original batteries was design, and an updated design requiring a new deep cycle battery and wiring harness was done on my first MS. I had three 12-volt batteries in that car. Subsequent to that it has been reported that Tesla has concluded that the 12-volt battery life is impacted by constant charging cycles.

The 12-volt battery runs things like the seat heaters, blower motors, electronics, etc., much of the car except the propulsion. The high voltage battery recharges the 12-volt battery, much like a generator or alternator on an ICE vehicle charges the car's battery. The design causes the 12-volt battery to cycle more than on an ICE vehicle, which "maintains the battery as it goes. Apparently the Tesla system allows the 12-volt battery to drop to a specified level, then performs the recharge process.

Apparently the solution is to replace the 12-volt battery annually. Apparently if you haven't had your small battery replaced yet, you will.

J.T. | 23. november 2015

Apparently the solution is to replace the 12-volt battery annually.

Doesn't really help someone who has had the car for only 4 months.

murphyS90D | 23. november 2015

I had my annual inspection in September and the 12 volt battery was not replaced.

rxlawdude | 23. november 2015

Apparently doesn't mean factually. Wild speculation does not imply reality.

Haggy | 23. november 2015

There were problems with some of the early batteries. Tesla replaced those as needed. There were issues with the software and charging algorithm. I never read any official announcement about what was done, but was told in Fremont that the next release (probably at some point before 6.2, but I don't remember specifically) would have software changes that would address the 12V battery.

I can't say how the battery charging algorithm works, but it's likely that if employees in Fremont were told that something was changing, then something was changed with respect to how it's done, and changed in order to get longer life from the battery. I assume that people whose job it is to work with the 12V charging system have paid particular attention to this issue, and that Tesla doesn't want to address it by changing out batteries on a regular basis rather than figuring out how to eliminate the problem.

Tesla's usual take on this sort of thing is that if they are making a software change and users aren't supposed to see a difference, there's no reason to announce anything. Had CU gone on about batteries instead of door handles, perhaps Tesla would have chimed in and we would have seen a vague one line tweet from Elon saying "battery issue was in the past, now fixed."

s.grot | 23. november 2015

I heard that problem is related to letting things plugged into the USB/12 v dc ports while parked because this puts load cycling on the 12 v battery | 23. november 2015

1) USB connections and 12v power connector disconnect when the car turns off. Use of these will have no effect to the 12v battery and are such low current as to have little effect when the car is powered.

2) This is not likely a 12v battery problem. The 12v battery rarely dies in a hour. I don't suspect the contactor as the car would not be drivable with a bad contactor. If the contractor had failed open, the car would have died while driving.

Most likely is the DC-to-DC inverter used to charge the 12v battery. If the inverter dies, once the 12v battery discharges, you'll have no power and the car appears "dead". The main battery is likely just fine.

Let us know what the final resolution is. | 23. november 2015

I should point out if the DC-to-DC inverter fails, draining the 12v battery may kill the 12v battery too, although the battery is not the cause of the problem.

FlatSix911 | 23. november 2015

Take a look at this thread on the TMC forum to read about 12V solutions

barrykmd | 23. november 2015

Doesn't really help someone who has had the car for only 4 months.

I had mine for 6 weeks before getting the warning. The problem is poor design. The constant current drain is just too much for a small lead-acid battery, but that still doesn't explain the very premature failures.

tmaz | 23. november 2015

I've had my 85D for 9 months and 34,000 miles. Knock on wood, I have not had any battery issues. Given the # of miles I put on the car, I couldn't justify doing the service every 12,000 miles. I plan to take it in for its first service around 48,000 miles. The fourth service will be my first service ;)

Iowa92x | 23. november 2015

Why is Tesla unable to resolve this 12v issue, years old now.

Bighorn | 23. november 2015

I don't think my 12V was replaced at my last annual visit--#2 at 61K miles.

Pungoteague_Dave | 23. november 2015

I wasn't being snarky. I was seriously told by service that the expected life of the 12-volt batteries is now 12-18 months. That's what I am planning. That's also confirmed by the link flatsix911 shows above. No need to jump on everything I post. I don't make this sh*t up - and am usually right, 99% of the time.

@bighorn, did you have a prior replacement?

Bighorn | 23. november 2015

I'd had two 12V replacements before that, though the most recent was a year and 38k miles before my most recent service.

Bluesday Afternoon | 21. januar 2016

It was my turn today. Got in my 85D this afternoon and was greeted with the message to replace my 12V battery. I almost made it to my 12,500 service appointment scheduled for 2/15/2016 but fell just short at 11,309 miles. Luckily, I only live 7 miles from the Costa Mesa Service Center and had the time to wait so I decided to just drop in without an appointment and hope for the best. They couldn't have been nicer. After a brief discussion about waiting until my scheduled appointment and deciding it wasn't worth the gamble they said it could take as long as two hours if I wanted to wait. Twenty-five minutes later I was back on the highway. Hardly had time to finish a second cup of hot chocolate but I did get to see a Model X. It was one of a number of photos rotating on the coffee machine's display.

Any one know how much a 12V replacement is out of warranty?

Bluesday Afternoon | 21. januar 2016

Didn't see the other thread by the same title or would have posted there. :-(

VideoGeek | 21. januar 2016

@Simply Red

Just paid $125.07 plus tax on a new battery for my out of warranty RWD S85

tes-s | 22. januar 2016

@VideoGeek - did that include installation? Which service center?

jordanrichard | 22. januar 2016

Ok, there has to be something other than a supplier issue at hand here. I took delivery in Mar 2014, have a hair over 39,000 miles and I am still on my original 12v battery.

I am sure Tesla has all the information they need to spot a common denominator amongst the cars with 12v battery issues.

Rocky_H | 22. januar 2016

@jordanrichard, I do wonder about that too. I got my car the same month you did, have 21K miles, and am also on my original battery.

GeorgeA | 22. januar 2016

Recommendations / options to Tesla:
1. Eliminate 12 volt battery, use main battery for everything, which doesn't need replacing every 12-18months
2. If keeping the 12v, increase it's size and quality to make it last much longer, 3 years at least, like other cars.
Perhaps the new Giga Factory can begin making these 12v batteries also to better control quality.
3. Update software to give us a warning sooner before 12volt dies so we can get it replaced when not on a trip.
4. If 12 volt dies, allow main battery to automatically jump start it and supply power temporarily to get to service.
5. If any above ideas not feasible , allow an easy jump start to 12v from another vehicle or portable power supply.

The last idea is a little humiliating to say the least if asking an ICE vehicle for a jump, since we have tons of power in the main battery but cannot use it currently when the 12 volt dies. Also a jump would tarnish the struggling public image of electric vehicles being dependable. Like many of you, I want to promote EVs in every way I can, not slow the migration away from ICE vehicles.

murphyS90D | 23. januar 2016

1. Not possible. The 12 volt battery activates the contactors that connect the HVB to the car.

4. See previous sentence.

5. The 12 volt battery jumper terminals are behind the nose cone. | 23. januar 2016

On option 2 - It's all tradeoffs. First there is no room in the current location (RWD) for a larger battery. It's also not clear that the battery has any quality issues. It appears the current design lasts about two years, but less or more depending on your amount and types of driving. Like any part, a small percentage fail prematurely.

Ok, let's go with a larger battery (although not feasible in existing cars) - it will be more expensive, weigh more and have a real effect in reducing range and may reduce cargo space if the car is redesigned around the larger battery. Some owners may be willing to have all these tradeoffs, but I expect many would not. It's a judgment call.

I'm not saying the Tesla has the best design, but there are tradeoffs that are made in any design choice like this.

Lastly the comment to make it last longer like other cars. BMW also has quite a few ICE models where the battery (much larger and more expensive that Tesla's battery) requires annual replacement. Just depends on what car you compare it with.

stevenmaifert | 23. januar 2016

12V batteries have been around a while. Hard to imagine at this point that Tesla hasn't found a supplier of a quality battery, whatever that means. I suspect there are systems in the MS that put unusually high current demands on the battery that necessitate more frequent charging cycles which leads to shortened battery life. Most manufacturers would view that as wear and tear. To Tesla's credit, they are replacing them as a warranted item at least for the duration of the new car warranty.

Pungoteague_Dave | 23. januar 2016

It isn't about quality. They fail due to the number and frequency of cycles. Think of them as akin to other disposables, like wipers.

robert.s.bjekich | 23. januar 2016

December 2013 - S 85 - 41,000 miles - original battery.

GeorgeA | 23. januar 2016

murphyS85: Future design improvements to the current 12v battery configuration or even eliminating it's need, should at least be on the table as new designs are considered. I believe they are. I agree it is all about trade offs. The Model S & X are wonderfully engineered and cutting edge in their high mileage long life main battery design. Yet the short lived 12v battery likely impacted Consumer Reports dependability rating factored into their disappointing down grade recommended rating. Most ICE batteries I have utilized over the years have lasted at least 3 years. I suspect Tesla wants to significantly extend the current 12v life, assuming it will be included in future designs.

stevenmaifert: Tesla is great at correcting or replacing any part such as 12v etc. They have the best customer service anywhere. I am as happy with my Model S as the day I got it 3 years ago.

I look forward to what new designs and long life/range main and 12v batteries come rolling out of the new Giga factory!

Shepbob | 24. januar 2016

My S85 (June 2015 delivery) had about 19K miles on Christmas Eve, when the 12V battery died with no notice.

Turned out the was a loose cable that somehow drained the battery in less than 3 hours.

The tow truck driver that Tesla sent out was able to get the car powered up by clamping his portable jumper battery on the Tesla's 12V terminals to drive it out of the garage, but it had to be towed to Fremont (closest SC).

Tesla diagnosed the problem in less than an hour, fixed the cable, and replaced the battery, all at no charge.

Compared to a lifetime of breakdowns and battery/alternator problems with ICE cars, this one was quickly and neatly resolved.

Anthony J. Parisio | 24. januar 2016

From reading all the post on this and other threads I have noticed something. Most of the people who have mentioned their battery needed replacing have mush lower miles than the people who haven't needed a replacement. I wonder if that is a factor. Of course we have not compared temperature zones.

So who lives in cool climate verses who lives in warm climate and did you need to replace you battery in two years?

stevenmaifert | 24. januar 2016

Bad Karma. So yesterday I post in this thread. This morning I go out to my MS and it presents me with the 12V Battery Needs Service, Replace Soon alert. Geez. This will be the second 12V battery in three years and 21K miles. I live in San Diego, so climate extremes is not the culprit. Good thing I already have an appointment at the SC for tomorrow morning as I got the Tire Pressure Monitoring System Needs Service alert two weeks ago. I love the great Tesla service, but wish I didn't have to experience it quite so often.

tes-s | 24. januar 2016

Most of the people who have mentioned their battery needed replacing have mush lower miles than the people who haven't needed a replacement.

Mine is 2.5 years old and 60k miles - getting battery replaced tomorrow.

But I think you are right - people with lower miles already had their battery replaced. More miles may have extended the life of the battery. Of course, now it is no longer under warranty.

tes-s | 24. januar 2016

Another interesting point - I got the replace 12v battery message upon returning from vacation and not driving the car for a week. First time in a long time I have not driven the car for a week.

Anthony J. Parisio | 24. januar 2016,

Maybe the 12V works harder and longer when the car sits. I only drive about 5000 miles a year. I had to replace it at 10,000 miles.

murphyS90D | 24. januar 2016

When the car is in motion the 12 volts is supplied by the DC-DC converter and also keeps the 12 volt battery topped off. When the car is parked the 12 volts is supplied by the 12 volt battery. The HVB is brought on line up to 5 times a day (last time I measured it) to recharge the 12 volt battery from about 50% to 100%. Charge cycles accumulate faster for a parked car and it will reach the cycle limit faster than a car that is always in motion. I would expect a low mileage car to need a battery replacement sooner than a high mileage car if the only criteria is the number of charge / discharge cycles.

tes-s | 24. januar 2016

10,000 miles - nice! Under warranty. :)

Bluesday Afternoon | 24. januar 2016

It's apparent no one on the Forum has an answer about the 12V battery issue and the magic trick to extend its usable life. Not sure if Tesla engineers know how or (maybe) they would provide guidance. I did leave my car unplugged for three days before the replace battery message appeared. I immediately went to the Tesla Service Center (about seven mile drive) and the message did not clear. I was kinda hoping the driving would recharge the battery enough to improve battery status. No luck! Too short a drive? I seldom leave my car unplugged and this was probably the longest series of days. I'd guess I've left my car unplugged, maybe, a total of ten days out of approximately 275 days of ownership.

I had a Porsche 911 SC for 13 years and would hook up a trickle charger to maintain the battery when it sat for more than 4-5 days (week days usually). Seemed to improve battery life. I wouldn't try this on my Tesla's 12v but I wonder if any owners have trickle charged the 12v and recovered the battery charge?

p.s. - 12v issues are certainly not an unusual event at the service center

jordanrichard | 24. januar 2016

Simply Red, no, no one here knows the answer. Only Tesla has the fleet wide metrics to identify a common denominator. As AP mentioned it may be a matter of low car usage, shortens the life. As I mentioned previously, come March I will have had my car for 2 years and I estimate that will have about 41,000 miles on my car by then.

VideoGeek | 24. januar 2016 The $125.07 price from the San Diego SC did not include tax or installation.

The life of the 12v battery depends upon a number of variables. The most important is the number and depth of discharge/charge cycles. The manufacturer’s data sheet ( shows that it can last over 6000 shallow cycles and yet fewer than 500 deep cycles.

The negative terminal lead has an Intelligent Battery Sensor (e.g. that the Tesla’s computer uses to monitor battery usage and health. What has Tesla learned from this data besides to move the battery to a more accessible location?

Empirical evidence indicates that the DC-DC converter is on and supplying current to the battery whenever the car is “awake” (i.e. handles out). The battery is supplying current to anything still active when the car is “asleep”.

I keep my car’s Energy Saving Mode set to ON (settings menu). My 12v battery lasted just over 51,000 miles and 26 months living primarily in a Southern California environment. I’m not sure what shortened/extended the battery’s life. Sometimes it sat parked (plugged in) in my garage but woke frequently when I walked by with the fob in my pocket. Did this add up to thousands of very shallow cycles? A few times it sat undisturbed in my garage while I was out of town. What cycling happened while I was gone? Other times the car was on almost continuously when I took it on an extended road trip.

What usage behaviors have other owner’s noted that may have impacted 12v battery life? How does “preconditioning” impact the cycle count? Does “camper mode” suck down the battery? How about using an inverter (12v DC to 115v AC) to power small appliances?

tes-s | 24. januar 2016

Did you install it yourself?