Another 12V flat battery

[tycanmt]

2021 4S : sitting in the garage for 3 weeks with main battery at 50% SoC.

Tonight I receive two phone calls (which I ignore because...telemarketers) that turn out to be from Porsche (actually Vodafone), saying that they think my Taycan might have been stolen or "sabotaged". We live in the middle of nowhere a mile up a snow covered track so if anyone stole the Taycan they're very good thieves. And of course it's sitting in the garage. But...can't unlock it. So the penny dropped: it stopped talking to the mothership which led them to believe someone had stolen it and disconnected the 12V battery. Sidebar: if they can call me when they detect it stops talking, why can't it send a "hey my 12V battery is low" message to ME yesterday!?!?!

Ok so I get on youtube and go through the resurrection process. Car is booted back up 20min later.

The section below is mainly aimed at Porsche/VAG engineers, assuming they are reading, but anyone else with some thoughts feel free to chime in.

But I'm wondering what exactly is the correct process to keep a Taycan alive longer than three weeks? Reading the doc, it implies (contrary to popular belief) that the 12V battery is absolutely not charged by the HV battery when the vehicle is parked. It says you need to charge it every 8 weeks. But then it says you need a charger that supplies 80A @ 14V. I may have such a charger, but I doubt many people have. But it also says to leave the vehicle plugged into a Level 2 charger when stored, with a 50% charge limit. Does that mean that the battery controller will charge the 12V battery even if the main battery is already charged to 50%?
This contradicts the advice to charge the 12V battery separately using the magic 80A charger. <confused> Also the doc says specifically NOT to use battery tenders, contrary to almost every single post on the internet. Right now I have it plugged in to my Level 2 charger, but how do I know when the 12V battery is fully charged?
I don't really want to just charge the HV battery to 80% because then I will need to drive the car (see above: snow) to run it back down to 50%.

For background: I do not have a dealer within 400 miles of me so I can't just roll in there and have them confuse me further then sell me a new 12V battery for $2000.

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[Dee]

Your 12V battery is charged by the HV battery.
No need for a trickle charger, don't screw up the proces in your car's software!
If the 12V battery isn't charged, there's something wrong with the software but generally you can leave it 4 weeks or even longer without any intervention.
Though, it is advised to start the car every two weeks to check the 12V readings:

13.4V: battery is charged, all good.
<13.0V: battery isn't charging, not good!
~14.4V: battery is charging by the DC/DC charger.

You can monitor the 12V battery in the right tube of the instrument cluster.

 

[f1eng]

After the same happened to me last Christmas I bought a lithium battery charger and connect it every week if I am not using the car.
It is irritating but easier than the tedious rigmarole associated with accessing the battery once it is in self protect mode. Whoever signed off that design certainly did not expect an owner to ever need it.

 

[Dee]

After the same happened to me last Christmas I bought a lithium battery charger and connect it every week if I am not using the car.
It is irritating but easier than the tedious rigmarole associated with accessing the battery once it is in self protect mode. Whoever signed off that design certainly did not expect an owner to ever need it.

Have you ever tested it after?
I tried one week, two weeks, three weeks etc.
It was fine, no problem whatsoever.

Once you regain confidence again you don't need to trickle-charge it but I can imagine you want reassurance.
It's not designed like that so whoever signed off that design isn't the one to blame imho.

PS I send you a PM last week, did you get it?

 

[prj]

The car should always charge the battery automatically if the HV has some juice left in it. The 8x "limit" is not a limit since the 2021 update afaik.
People have left Taycans for months without any issues.

So if you're going into 12V shutdown it's either a defective 12V (which with the LG Chem debacle is a common occurrence) - it thinks that there is 8Ah but actually it's much less, and when it goes to wake up the car it goes into low voltage shutoff - or there is some kind of error in a component preventing the car from connecting the HV contactor.

The 80 amp charger is exactly right, as with the trickle chargers you're not doing anything. The car consumes a massive amount of current when it wakes up, and it wakes up every now and then. That said, if everything is functioning correctly this should never be needed.

 

[Tooney]

The car should always charge the battery automatically if the HV has some juice left in it. The 8x "limit" is not a limit since the 2021 update afaik.
People have left Taycans for months without any issues.

So if you're going into 12V shutdown it's either a defective 12V (which with the LG Chem debacle is a common occurrence) - it thinks that there is 8Ah but actually it's much less, and when it goes to wake up the car it goes into low voltage shutoff - or there is some kind of error in a component preventing the car from connecting the HV contactor.

If the 12V battery is good, then there is something wrong with the 'auto charge the 12V battery' system and components.

There was a TSB - which I cannot locate - which mentioned a component external to the 12V battery - gateway ecu? - which, among other things, measures the charge in the 12V battery as part of the 'auto charge 12V battery' system. If that component is not functioning properly, it needs to be reset or replaced to prevent 12V from being discharged.

Problem is if battery is good (and Porsche has many TSBs about checking it thoroughly to confirm it is really bad before replacing it) then it may be difficult for dealer to diagnose whether the 'auto charge 12V battery system' is failing repeatedly or intermittently.

Good luck.

 

[f1eng]

The car should always charge the battery automatically if the HV has some juice left in it. The 8x "limit" is not a limit since the 2021 update afaik.
People have left Taycans for months without any issues.

So if you're going into 12V shutdown it's either a defective 12V (which with the LG Chem debacle is a common occurrence) - it thinks that there is 8Ah but actually it's much less, and when it goes to wake up the car it goes into low voltage shutoff - or there is some kind of error in a component preventing the car from connecting the HV contactor.

The 80 amp charger is exactly right, as with the trickle chargers you're not doing anything. The car consumes a massive amount of current when it wakes up, and it wakes up every now and then. That said, if everything is functioning correctly this should never be needed.

I am sure it should not be needed and I have been concerned from day 1 that both my 800V and 12V battery could be defective or degraded because mine was one of the cars left in storage for 4 or 5 months when the 12V battery was in short supply, meaning the 800V battery was not new when the car was delivered and there was a risk that the first batch of 12V batteries to arrive may have been rushed through QC.
Last Christmas my 12V had gone into self protect after 8 days not using the car. Plenty of other people on this forum reported similar experiences.
Now if I don't use the car for a week I put on the CTEK and it takes around 3 to 4 hours to charge reasonably well, I have never left it up the the fully charged light coming on.

Clearly it is bad and should not happen like this but it does and for quite a few owners, sadly.

 

[prj]

Clearly it is bad and should not happen like this but it does and for quite a few owners, sadly.

Then the battery is going to have to be replaced. You can't exactly put it on a CTEK if you leave the car at e.g. airport or some other place while you go on vacation, so this is not a reasonable solution.

 

[Mikegrr]

I believe you need a trickle charger if you leave the car sit for any length of time. I don’t care what Porsche says, the 12 volt is not charged by leaving the car attached to a level 2 charger. I experienced this myself when my 12 volt died. No notice from the Porsche app either.

 

[Dee]

I believe you need a trickle charger if you leave the car sit for any length of time. I don’t care what Porsche says, the 12 volt is not charged by leaving the car attached to a level 2 charger. I experienced this myself when my 12 volt died. No notice from the Porsche app either.

That doesn't apply for the majority of Taycans.
Obviously something isn't working like it should.
The only people who experience these kind of issues are on forums so it looks like a lot of people have these problems.
That's definitely not the case, this should be a problem of the past cuz it's fixed a long time ago.
So either you don't have the correct updates or your 12V battery is bad (which is unlikely).
If you have a warranty you should push Porsche to fix this.
Honestly....

 

[tycanmt]

Ok, a few replies re-stating the common beliefs about this, which empirically seem to not be valid, at least not for all cars. There was a similar post here a few weeks ago, so it's not just me.

But the diagram above was useful. I'm wondering if this is the vehicle's behavior:

1. 12V battery is supposed to be charged from the HV bus (so do not ever charge it directly -- this is consistent with Porsche's document, providing you don't have an 80A charger handy).
2. When exactly that charging happens is currently a mystery. It clearly isn't "as and when needed" because if that were true nobody would have a discharged 12V battery. Yet we do. Perhaps the mystery is shrouded in something like "it definitely charges when the vehicle's systems are fully turned on, and when the vehicle is charging, but otherwise kind of when it feels like it.

Perhaps the software that controls the "kind of when it feels like it" aspect above is buggy (hinted in the comment above about a TSB on 12V charging), or has some safeguards that turn out to produce false-positives? Furthermore, there seems to be a huge bug in that the car can't notify its owner that the 12V battery is running low.

I did notice the displayed voltage ramp myself last night when checking the car out post-charge, so it's good to have that confirmed (high voltage means "12V charging" while low voltage means "12V battery rail floating so fully charged"). Mine did revert to the float voltage after a few seconds.

 

[eddieterry]

I had the same symptoms this time last year. I used a lithium charger to get the 12 Volt back up to full - Porsche say not to leave it on maintenance just use it to bring up to charge and stop. I had Porsche check both 12 Volt and software - they found nothing wrong with either. Not had a repeat problem but then we have not had very cold weather (12 Volt does not like the very cold). Not sure if the algorithm has changed from 8 times charging to constant or not - something Porsche have not been definite on - I would hazard a guess it is still 8X as that would account for people having probs.

 

[tycanmt]

I had the same symptoms this time last year. I used a lithium charger to get the 12 Volt back up to full - Porsche say not to leave it on maintenance just use it to bring up to charge and stop. I had Porsche check both 12 Volt and software - they found nothing wrong with either. Not had a repeat problem but then we have not had very cold weather (12 Volt does not like the very cold). Not sure if the algorithm has changed from 8 times charging to constant or not - something Porsche have not been definite on - I would hazard a guess it is still 8X as that would account for people having probs.

Yes, you do need something to get the 12V Li battery (I think it's LFP) to boot back up. I used a donor AGM battery. Typically "chargers" don't work because they see zero volts and conclude no battery is connected. The "Lithium" 12V batteries aren't really batteries (obviously there are battery cells in there somewhere). They're a bunch of power electronics and a CPU running firmware that is hung off two terminals, trying to kind of impersonate a Lead Acid battery of yore. And now chargers are also a bunch of power electronics with a CPU with firmware. Together they do a good job of not achieving much of anything

For reference my vehicle was in a heated garage so temperature not an issue.

Obviously the 8X or whatever it is is knowable -- it'll be a constant in some source code file somewhere, or a config variable with a value set in the factory. What I wonder about however is whether that "charge so many times" actually achieves what a human would expect to occur. That would be something like: watch the 12V battery and if it seems discharged then wake up and charge it fully, so that it doesn't need charged again for several weeks. Rince/repeat N times.
Perhaps it doesn't do that. Perhaps it does something like: watch the 12V battery and if it seems like it is not fully charged, charge it up to full, and do that N times. The difference is that the second algorithm could potentially cycle every day. So for N==8 it would only take a week to give up charging.

The whole thing is a bit irritating as a software guy -- I can imagine exactly what kind of code this is, and exactly what kind of dude is responsible for it, and exactly how that dude would act if his bosses said "Hans (might be a woman, of course...) this seems to be all FUBAR why don't you go into the field for a couple of months, gather whatever logs you need, instrument the code further such as is needed to fully diagnose the problem, and get it fixed". I'm 100% sure that Hans's manager never said that and that's why we are all wasting endless hours holding seaweed over our cars trying to figure out how to make them hold charge.

 

[prj]

I would hazard a guess it is still 8X as that would account for people having probs.

It is not.

[*]When exactly that charging happens is currently a mystery. It clearly isn't "as and when needed" because if that were true nobody would have a discharged 12V battery. Yet we do. Perhaps the mystery is shrouded in something like "it definitely charges when the vehicle's systems are fully turned on, and when the vehicle is charging, but otherwise kind of when it feels like it.

It is not a mystery whatsoever and clearly stated - whenever the battery content drops below 8Ah.
If your battery is defective and the BMS thinks it has 8Ah, while it is much less, then as soon as the car wakes up to connect the HVB contactor, the battery will go into shutdown.

Let's just say 99% of people do not have any 12V issues and do not need any hacks of any kind.

 

[Mikegrr]

Because 99% do not leave their cars sit for extended periods.

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