Car won't start, dead 12v battery. Jump or service for new battery?

[TontoTaycan]

Due to the CA storms and holidays, etc. the car sat in the garage for a longer duration than normal. So the car is completely dead, and I'm assuming its the 12v.

Question is does this indicate it's a defective 12v battery, or is it normal for this car if it wasn't turned on for more than 5 weeks?

Should I just request a jump, and possibly be good to go like a normal ICE, or just turn it in to service and possibly get a new 12v battery?

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[Tooney]

Various approaches described in this thread: https://www.taycanforum.com/forum/t...ause-of-the-12-volt-problem….2529/#post-34471

 

[TontoTaycan]

Huge thanks for the reply, Tooney.

 

[Jayyvr890]

Still seems quite odd? I have a 5 year old BMW that I frequently don't use for 1-2 months and have never had a 12V failure.

Does your car have all the updates? Was it plugged into a charger for the 5 weeks?

 

[Tooney]

@TontoTaycan Also take a look at Agero's Porsche tips and videos. As well as other threads of how to's and photos on this forum.

 

[Vercingetorix]

A lithium jump pack is not supposed to be used.

 

[tchavei]

A lithium jump pack is not supposed to be used.

Mostly because there's a risk for the jump pack if not properly isolated as the on-board 12V battery will back feed a higher voltage than a traditional lead acid battery. Not to the car itself. I believe it's Porsche covering their butt in case you use some no name lithium booster and it bursts in flames after leaving it connected for too long.

We aren't really 'jump' starting the thing. Just powering the cpu so it boots up and starts charging the 12v battery by itself.

 

[800v]

Question is does this indicate it's a defective 12v battery, or is it normal for this car if it wasn't turned on for more than 5 weeks?

Well, I am currently trying to measure the voltage cut-offs and idle use based on the probable recharge behavior (see this post)

Let's assume the idle use of a Taycan is on average 0.15A (a wild guess! but maybe not too unreasonable, just a Blackvue dashcam uses about 0.3 to 0.4A by itself).

If your HV battery is above 10% (I assume so), the 12V 40Ah battery recharges at most 8 times from the HV battery, from 8Ah to 20Ah (at least, this is what we believe is the behavior). So, if you started with a full 12V battery (that is optimistic, from my initial measurements it seems usually about 50% or 60%), then you would get at most 40+8*12 = 136Ah energy (~ 1.8kWh, no problem for the HV battery). With a guessed idle use of 0.15A, that would be 136/0.15 = 906 hours =~ 38 days =~ 5.4 weeks!

So, I think it is quite normal -- if you leave a Taycan for more than 3 or 4 weeks you need to:
(1) either have someone start the car every two weeks for 15 minutes so the battery can both recharge, and you get a "fresh" 8 recharges again, or
(2) use a trickle charger on the 12V battery, or
(3) hook it up to a home charger (untested, but I think this will keep the 12V charged...).

(ps. if the idle use would be about 0.1A, then a Taycan could last about 8 weeks, and at 0.2A only 4 weeks; maybe idle use also depends on how well the 4G reception is?)

(ps2: please Porsche, make the 12V battery recharge many more times then 8 times!! No reason to not make it 100 times (~16kWh) -- we should expect the car to remain functional for at least 3 months with such a huge HV battery right there!)

 

[SergeyIndy]

Very interesting topic to me coming coming off of a totally bricked 12v on the Cayenne with total drain while a shop worked on the door strap that used accessory power and some relay was dead shut with no chance to charge it again. Still have 60 days to go to have my Taycan so apologies for the questions as I am trying to prepare for its arrival.

1. I thought Taycan can be started remotely similar to remote start from the App if away. Is this not the case so it reaches comfort temp inside by drive time.
2. What is the best trickle charger and I assume it works from the normal 120v outlet.
3. Would like to learn if connecting to home charger keeps 12v alive while on vacation looking at 2 weeks max.

 

[800v]

1. I thought Taycan can be started remotely similar to remote start from the App if away. Is this not the case so it reaches comfort temp inside by drive time.

Ah, right. Preheating remotely might be like a start and thus recharge and give 8 fresh recharges. If that works that would be awesome -- no more worries to go on a looong vacation not sure how to test this...

 

[Tooney]

The high voltage heater used for cabin preheating is reported to draw between 3 kw to 10 kw. Preheating is going to consume energy from HV battery. Not sure what impact it has on the 12V battery.

 

[Raphie]

But you can turn PH on, wait for app confirmation and cancel it again, you don’t need to sit out the whole process, It’s like a mouse cancelling a screen saver.
I don’t understand the 8x limit either, an arbitrary 16x limit would give it 2x the idle time.

 

[Scandinavian]

Ah, right. Preheating remotely might be like a start and thus recharge and give 8 fresh recharges. If that works that would be awesome -- no more worries to go on a looong vacation not sure how to test this...

Interesting line of thinking. The heating fan and electronics all work off the 12 volt battery so that will get extra supply from the HV battery. That can clearly be seen with a voltmeter on the 12 volt battery. So the battery will get some Charge during the duration the fan is running.

The question is though if the car will consider that as a full start. There was a reference to a certain terminal (15???). No idea on how we could determine if this happens by pre heating?

 

[tchavei]

The question is though if the car will consider that as a full start. There was a reference to a certain terminal (15???). No idea on how we could determine if this happens by pre heating?

That's easy to test. We just find a volunteer that will keep his taycan parked for 6 months while remotely starting preheating every 2 weeks.

In the meanwhile all organize to give him a loaner (leaf, zoe or similar) while he performs the test for us.

 

[Scandinavian]

That's easy to test. We just find a volunteer that will keep his taycan parked for 6 months while remotely starting preheating every 2 weeks.

In the meanwhile all organize to give him a loaner (leaf, zoe or similar) while he performs the test for us.

Sounds like you are offering to do this!

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