The charging battle btw Big Brother 800V and little Sister 12V

[Fadz]

Here are my $0.02 on the 12V EV issue my car was (is) plagued with.
A few weeks ago, my car had to be towed to the Dealer as the 12V battery was dead. (consequently, also damaged).

At that time no one knew what caused it. I was told i had a bad cell in the 12V battery.
Well now i have a new battery and it seems it is going slowly in the same direction.
To be fair i have to say now i have a dashcam installed so now i know for sure i have a draw during Parking. But i also have an additional 12V battery B130X for my Blackvue system to take the strain off the Porsch battery a little.
Either way here is what i came up with in regard to how my Porsche handles its little 12V "sister" battery.
It only charges the 12 Volt battery during...
1. Driving or when the engine is on (highest Charging power) 14-15V
2. DC or AC Charging of the big battery charges the 12V also but not as intense as driving. ~ 13V
3. And i also think when you precondition the car it will give its 12V sister a charge.

I wish the Porsche app would give out a battery reading of the 12V SoC. luckily my Blackvue Dashcam (app) does that so i can tell what the SoC of the 12V is at anytime from anywhere.

So, my advice to anyone who wants to make sure their 12V side of the car is not dead when they come back home after a few days or weeks. (OfCourse a nice Trickle charge if your car is parked inside is a smart thing while being away for longer.) But not all have a Garage for the car.
Next best thing: You are parked outside your house and have a Level 1 or 2 charger nearby. Advice. Keep it plugged in and have the cars big battery at a lower SoC.
MY approach is to set my Charging power to a lower 20Amps or such that's roughly about 5kW (more or less). Then change remotely when you feel like you want to give your 12V a charge remotely drag you charge level gage in the App from let's say %30 to %50 the first time and if needed again %50-%80 it would take longer to reach that with 5kW and thus charge your 12V longer as the process takes longer. If you can't control your charge power, then try out what works best for you. Technically you can also charge it up full (or almost) fast and then preheat your car regularly and that also charges your car but will of course use (waste more 800V energy) but that's ok as you have it charged up . You could technically hover btw the save %80 and down to %50 and back up. A strange workaround but it is an option if needed.

Allll this because Porsche it seems has not build in a Voltage threshold where it would kick in a charge of the 12V system to maintain it or recharge it before it reaches a dangerous low SoC.
At least that is what i had come up with so far. I hope i am wrong and there is a silver lining but so far i have not seen it.
I am actually German and grew up in Stuttgart. But i must say despite the Beauty of this car and its speed and handling. I am disappointed that my fellow German engineers did not think this through. (as far as i can tell)
Disclaimer: I reached out to Porsche in Germany and the ones i get on the phone. No one knows. %50 of the time i get rerouted to Porsche North America. And they know even less. As the Germans don't see an importance sharing things with their partners oversees or elsewhere.
Everyone is left guessing around.

I set my Dashcam to a voltage cut-off @ 12.5V just to be safe. the Bluackvue default i think is 12.1 V. But with the car and no "build in" Safety net you have to keep it higher. Let's see where this all goes.

I like the #1 info on how to charge 12v battery. Particularly, to just turn on the engine and charge automatically. This option is great especially when I'm away. The only drawback is i need to find somebody to turn on the engine. Yet, I need help on how to turn on the engine and keep it on while parked with door close.

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[BigApple]

I like the #1 info on how to charge 12v battery. Particularly, to just turn on the engine and charge automatically. This option is great especially when I'm away. The only drawback is i need to find somebody to turn on the engine. Yet, I need help on how to turn on the engine and keep it on while parked with door close.

That works usually only for about 30 or so minutes then the car goes back to sleep. Unless you are in drive mode. Maybe then it will stay on longer. I think the 60 min pre-climate option on the app is in my opinion the best step for remotely triggered charging of the car. It wastes extra heat or ac when on but a 1h (1x) session should give your cars 12v battery enough boost to last at least another day or more Of course depending on your actual added draw of dashcam for example. Set the heat or cooling to a temperature that uses the least power. So you won’t waste too much of the 800v energy. Even better is ofcourse having the car plugged in also. But that may not always be possible if you are away and your car is parked at the airport or so.
I hope one day porsche adds a 12V SoC reading to their app so you know when to actually trigger it. Or even better they add an automatic trigger of charge of the 12V battery when it goes below 12V. Then all this mess would go away.

 

[byebye]

Be careful with the external 12v power connection…
https://static.nhtsa.gov/odi/tsbs/2025/MC-11016721-0001.pdf

 

[SteveInKirkland]

Be careful with the external 12v power connection…
https://static.nhtsa.gov/odi/tsbs/2025/MC-11016721-0001.pdf

Thanks for posting that.

 

[BigApple]

Be careful with the external 12v power connection…
https://static.nhtsa.gov/odi/tsbs/2025/MC-11016721-0001.pdf

thank you. yes all 12v is coming in and being fed from the main 12 v power source. i wont mess or skip things by cutting corners.

 

[PrudentOcean]

pressure wave and corresponding sound generation

Engineering speak for explosion.

 

[BigApple]

here is a short update.
a few months ago i went to Stuttgart to talk to some folks over there at the "mothership" about my problem. Learned a lot about it. Bottom line "The BMS charges the 12V battery 2x then it gives up.

I Was told that back then in the summer. But who knows what changed till now. In every update things can change. And hopefully they will for the good. Explaining my problem to Them they Promised they will fix my issue. And indeed they did. What is unclear that the update was just for me or for everyone in an update they rolled out. My car is still at the dealership. (almost 3Months)
(But i don't think that is Porsches fault. ) Likely more on the dealership side (as they have to fix a rattling) hopefully soon. No complain over here as they gave me a brand new Macan loaner 4S. Either way i see my dashcam running ever since shortly after they applied the software update. And now 1.5 months later the dashcam is still being powered just fine through the 12V of the cars battery.
You will of course now loose on your SoC % daily. Not sure how much yet guessing +-1% a day in my scenario.
What i do wonder is if the car now just charges the 12V regardless of need or when it reaches the lower thresholds. That remains to be answered when i get my car back and get to my 12V Data readings from my gear installed.

 

[sor]

The thing that would be frustrating about this is we are talking a minuscule amount of energy. A dual channel dashcam should use 5-7 watts online, less in parking mode. That’s only going to take 0.2% of the HV battery per day to keep things topped off. Maybe there is a comparatively massive overhead in just bringing systems online to do the charge.

 

[BigApple]

The thing that would be frustrating about this is we are talking a minuscule amount of energy. A dual channel dashcam should use 5-7 watts online, less in parking mode. That’s only going to take 0.2% of the HV battery per day to keep things topped off. Maybe there is a comparatively massive overhead in just bringing systems online to do the charge.

In my case it is around 0.7Ah for my BlackVue dashcam (3cam) they record nonstop. And is also online nonstop.

that can drain a 12v battery fast depending on its capacity. And EV batteries I was told are on the lower end of capacity. But not sure exactly how many Ah the Macan battery actually has. I guess around 50-60 but not sure. Usually my battery is empty after 3 days. So that around fit.

 

[sor]

In my case it is around 0.7Ah for my BlackVue dashcam (3cam) they record nonstop. And is also online nonstop.

that can drain a 12v battery fast depending on its capacity. And EV batteries I was told are on the lower end of capacity. But not sure exactly how many Ah the Macan battery actually has. I guess around 50-60 but not sure. Usually my battery is empty after 3 days. So that around fit.

Ok, 0.7A @ ~12v is 8.4W. That's a tiny bit more than I had estimated based on research, but very close. You could push it to 10W assuming sometimes you have 12.5v or some variation. So rounding to 10W gives 240Wh required to run it for a day.

Just the straight math on this with a 95kWh battery backing the 12v low voltage battery (charging it as necessary), 240Wh/95kWh would imply a daily capacity drop on the High voltage battery pack of 0.25%, or 1% drop every four days. If you can't go weeks like this, and a larger daily drop is observed, it implies there's some overhead in supplementing the 12v that far outweighs keeping it topped off.

 

[sor]

Just the 12v alone, if it were say 60Ah, that's 60 * 12 = ~720Wh. So you'd only be able to run the dash cam at 240Wh for ~3 days before draining that LV battery completely.

 

[pm4s]

Just the 12v alone, if it were say 60Ah, that's 60 * 12 = ~720Wh. So you'd only be able to run the dash cam at 240Wh for ~3 days before draining that LV battery completely.

If you drop below 12v the car may not start so you can’t drain your battery over 50%
See my post here:
https://www.macanevowners.com/forum/threads/220v-socket-in-the-trunk.23920/#post-354774

 

[sor]

If you drop below 12v the car may not start so you can’t drain your battery over 50%
See my post here:
https://www.macanevowners.com/forum/threads/220v-socket-in-the-trunk.23920/#post-354774

Of course, but in terms of calculating the capacity the math holds. This is good to keep in mind but also why I said “before draining completely”.

 

[BigApple]

If you drop below 12v the car may not start so you can’t drain your battery over 50%
See my post here:
https://www.macanevowners.com/forum/threads/220v-socket-in-the-trunk.23920/#post-354774

Correct. At some point when it goes below a certain point the car goes offline. To keep the basic functions alive. But nothing remotely works anymore. Seen it firsthand.

 

[BigApple]

Just the 12v alone, if it were say 60Ah, that's 60 * 12 = ~720Wh. So you'd only be able to run the dash cam at 240Wh for ~3 days before draining that LV battery completely.

Yep that is what I get around 3 days before the 11.7v are reached

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