How to prevent 12v battery from dying when stored for 6 weeks without trickle charger or charging station?

[JohnPM]

There's a video on youtube by a Porsche dealer connecting a charger to the 12v. They show you where to push in the lock mechanism to trick the car into thinking the frunk is closed.

This one, perhaps:

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[SteveDC]

my 2024 ct turbo left at 55% soc was flat within 12 days at xmas. underground garage likely between 2-7 c. why on earth the hv battery won't keep the 12v in shape. one comes back to a dead 12v and 50+ % of charge. beyond dumb. Also, how is it some can leave it for 6 weeks with no issues...

AFAIK, there is not a consensus on the forum about how many times the HV battery will recharge the 12 V when the vehicle is stored. I think I’ve seen 6 times when the main battery is stored at over 50%, with a caution not to store at much high percentages, so as to permit the battery management system to rebalance to individual cell, so say 50% - 60%. I kind of wish we had a firm rule we could count on. Don’t use the app, keep the key away, and 50-60% seem to be the only guides, but they don’t always work, based on my own experience.

 

[Clarkes1]

I’ve had a problem with the 12v battery on my MY23 CT since I got the car (June ‘23). Leaving the car on 3 or 4 occasions for spells between 1 to 9 weeks and coming back, unable to unlock and calling out the Porsche Roadside assistance each time.

Anyway, mid December I took the car into the dealer, asked them to check it over. They did some checking and said the battery was fine. Knowing this was not the case I said keep it for a few weeks, stick it in the corner of the garage, don’t touch it, open it or drive it anywhere and try again after ~2 weeks. After 2 weeks, lo and behold the car could not be unlocked, powered up and the battery voltage had dropped below the operating threshold; this was last week.

latest is that Porsche are now replacing the HV converter. I’m hoping this will solve the slow discharge issue from the 12v and keep it topped up from the big HV battery.

 

[exilen94]

I’ve had a problem with the 12v battery on my MY23 CT since I got the car (June ‘23). Leaving the car on 3 or 4 occasions for spells between 1 to 9 weeks and coming back, unable to unlock and calling out the Porsche Roadside assistance each time.

Anyway, mid December I took the car into the dealer, asked them to check it over. They did some checking and said the battery was fine. Knowing this was not the case I said keep it for a few weeks, stick it in the corner of the garage, don’t touch it, open it or drive it anywhere and try again after ~2 weeks. After 2 weeks, lo and behold the car could not be unlocked, powered up and the battery voltage had dropped below the operating threshold; this was last week.

latest is that Porsche are now replacing the HV converter. I’m hoping this will solve the slow discharge issue from the 12v and keep it topped up from the big HV battery.

Is there a way to see the charge level of the 12v battery?

 

[Clarkes1]

When you are driving the car you can get the voltage displayed. I don’t think you can get it via the app remotely.

 

[Dee]

My 12V battery didn't die in three weeks so I think my car is ok.
I've seen other people do three months.
If all works as intended it shouldn't drain at all, even if you check your app.
You can test it: leave it untouched for a week or two and if it still works you're ok for the rest of the time.

 

[exilen94]

When you are driving the car you can get the voltage displayed. I don’t think you can get it via the app remotely.

The voltage was 13.4 or 13.6 when I turned on the car, is that good?

 

[Clarkes1]

The voltage was 13.4 or 13.6 when I turned on the car, is that good?

Yes I would say so. I recall the ‘12v’ battery fully charged is around 14v and the Porsche Assist guy indicated if it drops to around 11v then it doesn’t have enough to operate the doors etc. it’s a relatively small discharge (drop in voltage) before it’s game over.

 

[Clarkes1]

My 12V battery didn't die in three weeks so I think my car is ok.
I've seen other people do three months.
If all works as intended it shouldn't drain at all, even if you check your app.
You can test it: leave it untouched for a week or two and if it still works you're ok for the rest of the time.

Yes. It’s got to be a fault on my car. It’s somewhat ridiculous to be advised you have to plug it into a trickle charger when you go away for a few days.

 

[Donlam]

Top ups only occur a fixed number of times (and scenarios) and can't be relied upon. I think there is something on this topic buried in one of the threads which explains more. MY is entirely irrelevant as it was introduced by a software patch to all models which didn't already have it.

Owner's manual:

The top up might occur a certain number of times. It was in Sept - Oct for 6 weeks and exposed to direct sunlight as well. But believe it or not my car is fine since day one.
Cars are design to work outdoor anyway.

 

[W1NGE]

Is there a way to see the charge level of the 12v battery?

Information menu item in right tube on main display and ensure that of the items selected ,(see PCM displays) that 12v battery is one of them

 

[W1NGE]

Yes I would say so. I recall the ‘12v’ battery fully charged is around 14v and the Porsche Assist guy indicated if it drops to around 11v then it doesn’t have enough to operate the doors etc. it’s a relatively small discharge (drop in voltage) before it’s game over.

13.6v

 

[figure1a]

You can ask them to turn it on for 5-10mins every week. That should reset the 12v charging process.

No need. The car automatically tops off the 12v with power from the HV if the 12V starts to lose voltage.

 

[exilen94]

13.6v

It means that it shows 13.6 if it is fully charged?
When I started my car, it seem to regulate between 13.4 and 13.6 when standing still

 

[f1eng]

It means that it shows 13.6 if it is fully charged?
When I started my car, it seem to regulate between 13.4 and 13.6 when standing still

I fear by the time the right tube display is switched on the HV battery has already started charging the 12V so what is displayed is the charger output.
Mine read 13.4 immediately after my car was jump started by Porsche assist even though in fact the 12V battery did not have enough voltage to unlock the car 30 seconds previously.

So yes, there is a display but it never connected, as far as I can see, in such a way as to display the non-running state of charge of the 12V battery.

I do have car scanner app and a dongle but have only used it a couple of times to look at main battery SOH, maybe I should do more investigations. Funnily enough the main reason I haven't used it much is so it doesn't flatten the 12V battery.

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