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

[whitex]

Yes. Not Porsche Taycan - but from Audi e-tron GT, somewhat wordy 'self study' manual (I guess for their service tech's). Anyway same under the skin....

"terminal 15 cycle = basically ignition-start button on/off"

This might have changed since the above was written, however, if it still works like this, there seems to be a simple workaround for long term storage. The key is in the sentence "This process can be repeated 8 times per terminal 15 cycle". In other words, you just have to cycle terminal 15 to reset the 8 recharge limit, which can be done by scheduling a preconditioning timer. So, if you leave your car plugged in to EVSE, so the HV battery will always top off, you can set a preconditioning timer once a week, or however often you want to reset the 8 cycle limit. This should allow for years of storage without issues. As a side note, it might also be possible that just topping off the HV battery also counts as terminal 15 cycle, but I am not sure of that.

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[simcity]

In other words, you just have to cycle terminal 15 to reset the 8 recharge limit, which can be done by scheduling a preconditioning timer. So, if you leave your car plugged in to EVSE, so the HV battery will always top off, you can set a preconditioning timer once a week, or however often you want to reset the 8 cycle limit. This should allow for years of storage without issues. As a side note, it might also be possible that just topping off the HV battery also counts as terminal 15 cycle, but I am not sure of that.

Are you certain of that?

I'm not sure that counts as a terminal 15 cycle. They define Terminal 15 as "= ignition ON = ready for operation; also referred to as “switched positive” "

Although the HV system may be otherwise energised for pre-conditioning - this may not necessarily be a Terminal 15 counted "event"...

 

[whitex]

Are you certain of that?

I'm not sure that counts as a terminal 15 cycle. They define Terminal 15 as "= ignition ON = ready for operation; also referred to as “switched positive” "

Although the HV system may be otherwise energised for pre-conditioning - this may not necessarily be a Terminal 15 counted "event"...

90%, IIRC even my 12V cigarette lighter comes to life when pre-conditioning. I'd have to find the actual true Terminal 15 and probe it.

 

[simcity]

90%, IIRC even my 12V cigarette lighter comes to life when pre-conditioning. I'd have to find the actual true Terminal 15 and probe it.

Yeah it’s a fine line of distinction. Here’s my thinking. You initiate say preconditioning and the car wakes up the HV subsystem to crank up the Webasto heater module. Also it cranks up the 12V subsystem to run the rest of the HVAC etc. No doubt the 12v battery would be charged as part of this process.

However, crucially does the infamous Terminal 15 get triggered as a cycle count. Hence then resetting the 8 cycle full recharge count to the beginning, iyswim?

So the battery yes might get a short term charge whilst pre-con is running, maybe 15 mins or so, but if it’s say already on the 8th ordinary attempt at recharge - it’s as if the battery charge algorithm doesn’t see the car as being “ignition on = ready for operation” - then it may not ever get another recharge attempt….meanwhile the car still sitting there.

 

[Dee]

I don't have exact figures but during this 5 months it dropped from 80 to 65 because I let it circulate the coolant, heat the cabin and battery for two times. Then charged from 65 to 70 - just for testing.. Still showed 70% today.
If the key is not nearby and you don't wake it remotely - it does not use much.
My Porsche connect has ended long time ago.

So that's not setting a record.
If you power the car up, it'll charge, no matter what.
An EV doesn't need to drive to charge the 12V battery.
The question is, how long does the 12V battery stay healthy if left in storage unattended?

 

[whitex]

The question is, how long does the 12V battery stay healthy if left in storage unattended?

This will depends on amount of battery drain, which will depend on cellular coverage (modems can use more power when in poor coverage), how often app connects, whether or not you have a dashcam (even Porsche OEM dashcam operates 24/7), how often the cloud pushes an OTA (however minimal it is). Last but not least, it will depend on starting 12V battery SoC, its age, and ambient temperatures.

 

[Dee]

This will depends on amount of battery drain, which will depend on cellular coverage (modems can use more power when in poor coverage), how often app connects, whether or not you have a dashcam (even Porsche OEM dashcam operates 24/7), how often the cloud pushes an OTA (however minimal it is). Last but not least, it will depend on starting 12V battery SoC, its age, and ambient temperatures.

Irrelevant.
As long as the HV battery is charging the 12V battery it's ok, no matter how much drain the 12V battery has.

 

[whitex]

Irrelevant.
As long as the HV battery is charging the 12V battery it's ok, no matter how much drain the 12V battery has.

Then you answered your own question - it will stay ok as long as it's being automatically topped off from HV battery, then it will just die of all age eventually. I assumed by unattended you meant left alone, no recharging.

 

[Dee]

Then you answered your own question

No, I answered the OP's question.

 

[007]

I just returned from a 5 week trip and the car came alive with no issue. No drop in battery, was left at a 55% charge, unplugged, unlocked.

 

[exilen94]

I just returned from a 5 week trip and the car came alive with no issue. No drop in battery, was left at a 55% charge, unplugged, unlocked.

That’s great, did you check Porsche app while you were away?

 

[Clarkes1]

Looks like I may have the storaging record here as my 4S was put in garage 30.8.2024. So it has now stayed there ca. 5 months. Charged once from 65 to 70%.
Powered on 2-3 times just to check there's no errors and reset the 12V charging cycles. It has no warming in the garage so temp. has been all between +25C to -25C.
No problems with the 12V since converter and charger changed.
Earlier I had several 12V flatouts.

I’m having my HV converter changed also, but what do you mean when you refer to the ‘charger being changed. ?

 

[Art]

OBC ie. on board charger was changed too. I had DC charging fail too.

5 pages about the whole 8 months repair.
https://www.taycanforum.com/forum/threads/1-year-gone-electrical-system-fault.19064/

 

[007]

That’s great, did you check Porsche app while you were away?

Not this time… but I do these extended trips a few times a year, and I’ve checked in app the past. Didn’t notice any difference in battery life when checking; no drop in charge or issues coming alive.

The only thing I notice is how nice the car drives after being away so long ?

 

[exilen94]

Not this time… but I do these extended trips a few times a year, and I’ve checked in app the past. Didn’t notice any difference in battery life when checking; no drop in charge or issues coming alive.

The only thing I notice is how nice the car drives after being away so long ?

Did the car get back to normal after driving or something had to be serviced?

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