Dead 12 Volt Battery recharging and towing questions

[DMTonka]

I have stored my '21 Taycan in an unheated garage for three winters. Each year I have set the charging profile at 50% and plugged it in for 24-36 hours every 3-4 weeks.

Year 1 - No problems, when i was ready to use it again it turned on like normal.

Year 2 - When I was ready to use it again I had a dead 12 Volt battery. Thanks to this forum I found the posts about the process to manually open the door, use a battery charger on the kick panel terminal to open the frunk, then use the battery charger to wake up the 12 Volt battery so that I could plug in the my wall charger and recharge both the high voltage batteries and the 12 volt batteries. After jumping through those hoops everything eventually worked normally.

Year 3 - Two weeks ago when I went to plug it in I saw symptoms of dead 12 volt battery. I went through the hoops above and since I was not ready to take it out of storage I just left it plugged into the regular wall charger (Grizzly 40A) for 48 hours. Unplugged it and everything looked fine.

Yesterday I went to plug it in to change the profile back up to 80% charge because we were going to start driving it again and it was showing all the signs of a dead 12 Volt battery again. But this time, it didn't come back to normal. I was using a Schumacher Charger and when I would disconnected it from the charging posts in the frunk everything would turn off again. This happened repeatedly. I was finally able to get everything to stay on long enough for me to change the charge profile to direct charge and then when I plugged in the wall charger it started charging the high voltage packs so I figured I was in the clear. This morning I went to turn it on and got nothing again, everything was dead. I connected to 12 volt charger to the posts in the frunk and then the PCM would come on briefly and it said the high voltage batteries were 97% charged but as soon as I unplugged the 12volt battery everything shut down again.

At this point it seems clear that my 12 volt battery is probably damaged so there is no mystery there but I have a few other questions for you all...

1. Is there a consensus on using a trickle charger for the 12 volt battery for long term storage? Older thread seem split on this.

2. In situations like this what setting should be used to recharge the 12 Volt battery? My charger has a 2 Amp, 15 Amp, or Jump Start setting. Is it better to let it sit overnight at 2 Amps or use the higher current settings briefly and then plug in the High Voltage charger?

3. Instead on my Schumacher charger should I have used a Portable Jump Starter? The tow truck driver hooked up a JNC660 1700 Peak Amp jumper pack to the terminals so I was able to back it out of my garage so he could hook it up to his tow truck. It seemed like the system came back closer to normal with that unit than my Schumacher charger.

4. If he wouldn't have had the jumper pack I am not sure how we could have gotten it moved from my garage because I had it parked pretty close to some other items. Is there a way to manually put the car in Neutral when the electrical system is bricked? My BMW X5 has a cupholder that can be removed and there is a special tool that can be used to manually put it in neutral when the electronics fail. Is there anything like that on the Taycan.

Thanks to everyone that has posted on these topics in the past. It really helped me be calm as I was dealing with this to know that I wasn't the only one who's had these challenges.

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[Hirschaj]

I have stored my '21 Taycan in an unheated garage for three winters. Each year I have set the charging profile at 50% and plugged it in for 24-36 hours every 3-4 weeks.

Year 1 - No problems, when i was ready to use it again it turned on like normal.

Year 2 - When I was ready to use it again I had a dead 12 Volt battery. Thanks to this forum I found the posts about the process to manually open the door, use a battery charger on the kick panel terminal to open the frunk, then use the battery charger to wake up the 12 Volt battery so that I could plug in the my wall charger and recharge both the high voltage batteries and the 12 volt batteries. After jumping through those hoops everything eventually worked normally.

Year 3 - Two weeks ago when I went to plug it in I saw symptoms of dead 12 volt battery. I went through the hoops above and since I was not ready to take it out of storage I just left it plugged into the regular wall charger (Grizzly 40A) for 48 hours. Unplugged it and everything looked fine.

Yesterday I went to plug it in to change the profile back up to 80% charge because we were going to start driving it again and it was showing all the signs of a dead 12 Volt battery again. But this time, it didn't come back to normal. I was using a Schumacher Charger and when I would disconnected it from the charging posts in the frunk everything would turn off again. This happened repeatedly. I was finally able to get everything to stay on long enough for me to change the charge profile to direct charge and then when I plugged in the wall charger it started charging the high voltage packs so I figured I was in the clear. This morning I went to turn it on and got nothing again, everything was dead. I connected to 12 volt charger to the posts in the frunk and then the PCM would come on briefly and it said the high voltage batteries were 97% charged but as soon as I unplugged the 12volt battery everything shut down again.

At this point it seems clear that my 12 volt battery is probably damaged so there is no mystery there but I have a few other questions for you all...

1. Is there a consensus on using a trickle charger for the 12 volt battery for long term storage? Older thread seem split on this.

2. In situations like this what setting should be used to recharge the 12 Volt battery? My charger has a 2 Amp, 15 Amp, or Jump Start setting. Is it better to let it sit overnight at 2 Amps or use the higher current settings briefly and then plug in the High Voltage charger?

3. Instead on my Schumacher charger should I have used a Portable Jump Starter? The tow truck driver hooked up a JNC660 1700 Peak Amp jumper pack to the terminals so I was able to back it out of my garage so he could hook it up to his tow truck. It seemed like the system came back closer to normal with that unit than my Schumacher charger.

4. If he wouldn't have had the jumper pack I am not sure how we could have gotten it moved from my garage because I had it parked pretty close to some other items. Is there a way to manually put the car in Neutral when the electrical system is bricked? My BMW X5 has a cupholder that can be removed and there is a special tool that can be used to manually put it in neutral when the electronics fail. Is there anything like that on the Taycan.

Thanks to everyone that has posted on these topics in the past. It really helped me be calm as I was dealing with this to know that I wasn't the only one who's had these challenges.

I can only comment on question 1. The manual seems very clear about using a trickle charger if in storage for longer than 6 weeks.

 

[KLHubb]

I wonder whether the undercharge protection has been triggered?
See the attached text from the Porsche Charge-o-mat Pro.
This is the unit specifically recommended for Porsches with Li-ion batteries.

 

[r553]

I bought a CTEK lithium suitable trickle charger in case my 12 volt battery went dead. I keep in my trunk and it's karma keeps the 12 volt battery happy apparently.

 

[Gino]

I have stored my '21 Taycan in an unheated garage for three winters. Each year I have set the charging profile at 50% and plugged it in for 24-36 hours every 3-4 weeks.

Year 1 - No problems, when i was ready to use it again it turned on like normal.

Year 2 - When I was ready to use it again I had a dead 12 Volt battery. Thanks to this forum I found the posts about the process to manually open the door, use a battery charger on the kick panel terminal to open the frunk, then use the battery charger to wake up the 12 Volt battery so that I could plug in the my wall charger and recharge both the high voltage batteries and the 12 volt batteries. After jumping through those hoops everything eventually worked normally.

Year 3 - Two weeks ago when I went to plug it in I saw symptoms of dead 12 volt battery. I went through the hoops above and since I was not ready to take it out of storage I just left it plugged into the regular wall charger (Grizzly 40A) for 48 hours. Unplugged it and everything looked fine.

Yesterday I went to plug it in to change the profile back up to 80% charge because we were going to start driving it again and it was showing all the signs of a dead 12 Volt battery again. But this time, it didn't come back to normal. I was using a Schumacher Charger and when I would disconnected it from the charging posts in the frunk everything would turn off again. This happened repeatedly. I was finally able to get everything to stay on long enough for me to change the charge profile to direct charge and then when I plugged in the wall charger it started charging the high voltage packs so I figured I was in the clear. This morning I went to turn it on and got nothing again, everything was dead. I connected to 12 volt charger to the posts in the frunk and then the PCM would come on briefly and it said the high voltage batteries were 97% charged but as soon as I unplugged the 12volt battery everything shut down again.

At this point it seems clear that my 12 volt battery is probably damaged so there is no mystery there but I have a few other questions for you all...

1. Is there a consensus on using a trickle charger for the 12 volt battery for long term storage? Older thread seem split on this.

2. In situations like this what setting should be used to recharge the 12 Volt battery? My charger has a 2 Amp, 15 Amp, or Jump Start setting. Is it better to let it sit overnight at 2 Amps or use the higher current settings briefly and then plug in the High Voltage charger?

3. Instead on my Schumacher charger should I have used a Portable Jump Starter? The tow truck driver hooked up a JNC660 1700 Peak Amp jumper pack to the terminals so I was able to back it out of my garage so he could hook it up to his tow truck. It seemed like the system came back closer to normal with that unit than my Schumacher charger.

4. If he wouldn't have had the jumper pack I am not sure how we could have gotten it moved from my garage because I had it parked pretty close to some other items. Is there a way to manually put the car in Neutral when the electrical system is bricked? My BMW X5 has a cupholder that can be removed and there is a special tool that can be used to manually put it in neutral when the electronics fail. Is there anything like that on the Taycan.

Thanks to everyone that has posted on these topics in the past. It really helped me be calm as I was dealing with this to know that I wasn't the only one who's had these challenges.

Each year you allowed your 12 volt battery to degrade by not keeping the main battery charged to at least 50% which allows the 12v battery to be charged by the main battery from what Porsche has told me.
After 2 years of the 12v battery getting completely drained it is not a surprise you will need to replace the 12v battery because it will no longer hold a charge.
You could put a trickle charger on the 12v battery but I would instead make sure your main battery never gets below 50%. I'm sure it's not good for the main battery to get too low for too long either which I would assume will reduce it's lifespan as well at a much higher cost than the 12v battery that controls the system. Good luck.

 

[Dr Bob]

........but I would instead make sure your main battery never gets below 50%. I'm sure it's not good for the main battery to get too low for too long either which I would assume will reduce it's lifespan as well at a much higher cost than the 12v battery that controls the system.

You are right to question depleting the 12V battery to zero. That is a killer for Li Ion batteries. I certainly would not do this by design.

You are totally wrong on saying the main battery should never get below 50%. The problem at low SoC is getting the battery cells into the lower voltage knee. This is below 20% or maybe 10-15% if there is a good buffer, which is what a number of posters have said. If you are in the voltage knee then you run into balance issues and one cell could get to zero before the others and wreck the cells. Hence dont take the 12V to zero but you can easily run the main battery down to 20%. Holding an Li Ion battery at 30% is a good way to store them.

 

[DMTonka]

Each year you allowed your 12 volt battery to degrade by not keeping the main battery charged to at least 50% which allows the 12v battery to be charged by the main battery from what Porsche has told me.
After 2 years of the 12v battery getting completely drained it is not a surprise you will need to replace the 12v battery because it will no longer hold a charge.
You could put a trickle charger on the 12v battery but I would instead make sure your main battery never gets below 50%. I'm sure it's not good for the main battery to get too low for too long either which I would assume will reduce it's lifespan as well at a much higher cost than the 12v battery that controls the system. Good luck.

Hi Gino,
The main batteries always held their charge, whenever I would plug it while storing it. The PCM indicated that the batteries would drop only 1-2% over several weeks of storage. I would still leave it plugged in for a few days with the expectation that although the main batteries were charged (to 50% per my profile setting) that plugging it in I was also allowing the system to keep the 12 volt batteries charged.

This was obviously not enough maintenance for the 12 volt system hence the tow truck visit yesterday.

The issue was not with the main batteries being below 50% because they always were in that neighborhood.

 

[Gino]

You are right to question depleting the 12V battery to zero. That is a killer for Li Ion batteries. I certainly would not do this by design.

You are totally wrong on saying the main battery should never get below 50%. The problem at low SoC is getting the battery cells into the lower voltage knee. This is below 20% or maybe 10-15% if there is a good buffer, which is what a number of posters have said. If you are in the voltage knee then you run into balance issues and one cell could get to zero before the others and wreck the cells. Hence dont take the 12V to zero but you can easily run the main battery down to 20%. Holding an Li Ion battery at 30% is a good way to store them.

I was given Porsche service Bulletin #: 2003.1 by a Taycan owner several months ago which states:
"Set the high-voltage battery to charge to 50% to reduce aging and wear and tear of the high-voltage battery"

My Porsche dealer was not aware of this bulletin wheh I showed it to them but they verified it was correct.

The bulletin also states:

Connect the vehicle to suitable Level 2 electric vehicle supply equipment (the Porsche Mobile Charger or Mobile Charger Connect, for example)

9. Lock the vehicle using the key remote

10. Store the vehicle key at least 30 feet (10 meters) away from the vehicle

11. Avoid repeated or prolonged use of the My Porsche smartphone app. Establishing a connection between the
app and the vehicle can lead to a discharged 12-volt battery

12. If possible, ambient temperature for the vehicle should be between approx 32 and 68°F(0-20°C)during storage

13. The 12-volt Lithium-Ion battery must be charged every 8 weeks the vehicle is in storage.

I don't allow my battery to sit in storage below 50% any longer after being given this service bulletin. I was also told the software in the vehicle allows the 12v battery to be charged by the main battery only when the main battery is at 50% or higher charge state which my dealer told me.
I am still trying to see if there is a Porsche Service Bulletin which states this but I may have to reach out to Porsche Engineering in Germany to get confirmation of this information.

 

[Gino]

Hi Gino,
The main batteries always held their charge, whenever I would plug it while storing it. The PCM indicated that the batteries would drop only 1-2% over several weeks of storage. I would still leave it plugged in for a few days with the expectation that although the main batteries were charged (to 50% per my profile setting) that plugging it in I was also allowing the system to keep the 12 volt batteries charged.

This was obviously not enough maintenance for the 12 volt system hence the tow truck visit yesterday.

The issue was not with the main batteries being below 50% because they always were in that neighborhood.

I've asked Porsche multiple times if I should or could set up a trickle charger on my 12v battery since I won't have a 220v charger in my garage until I can figure out how to run 220v to my garage without digging up the driveway between my townhome & my garage. Until then they told me to just make sure I am charged to at least 50% and my 12v battery will be fine. So far we have had no problems but we do drive out Taycan every week and at most leave it in the garage when traveling at the most for 30 days. So far no issues. All I know is no batteries like to be left in a low charge state for very long before the battery life begins to degrade. What charge level is too low and for how long is something I'm going to find out as my Taycan gets closer to it's 8 year warranty but I would expect I will end up replacing the 12v battery at the 5-6 year mark like any other starting battery but I do hope it lasts longer which will tell me the Porsche charging strategy for the main & 12v batteries is sound. Hopefully someone else on this forum will have additional information to add...

 

[Tooney]

Latest TSBs for storage.
For owners: https://static.nhtsa.gov/odi/tsbs/2022/MC-10209809-0001.pdf
For dealers for cars prior to owner: https://static.nhtsa.gov/odi/tsbs/2022/MC-10209808-0001.pdf
Both describe using charger for the 12volt battery:

The 12-volt battery must only be charged using a suitable battery charger that has a current and voltage-controlled charge map. To guarantee a sufficient charge, it is recommended to charge the vehicle electrical system battery as follows:​

• Voltage:14.4 V​

• Charge current: 80 A​

• Charging time: at least 65 minutes​

Second one says:

The 12-volt vehicle electrical system battery is charged automatically via the high-voltage battery. The Charge-o-mat and Charge-o-mat Pro must not be used on Taycan vehicles.​

 

[raharris]

I believe it’s a little unclear in the TSB still; it does not clarify if the 12v is only charged when the car is in drive or also when the vehicle is parked as the HV battery isn’t active?

OP I assume your charger is compatible with lithium ion? My c-tek has a button to reset the battery electronics if a battery state gets to low.

 

[Gino]

I've asked Porsche multiple times if I should or could set up a trickle charger on my 12v battery since I won't have a 220v charger in my garage until I can figure out how to run 220v to my garage without digging up the driveway between my townhome & my garage. Until then they told me to just make sure I am charged to at least 50% and my 12v battery will be fine. So far we have had no problems but we do drive out Taycan every week and at most leave it in the garage when traveling at the most for 30 days. So far no issues. All I know is no batteries like to be left in a low charge state for very long before the battery life begins to degrade. What charge level is too low and for how long is something I'm going to find out as my Taycan gets closer to it's 8 year warranty but I would expect I will end up replacing the 12v battery at the 5-6 year mark like any other starting battery but I do hope it lasts longer which will tell me the Porsche charging strategy for the main & 12v batteries is sound. Hopefully someone else on this forum will have additional information to add...

It is also clear from Porsche that I am not to charge with the 120v cable that came with my vehicle or even the new one which they are replacing for free for more than 12 hours at a time.
I was told by Porsche charging at 120V for long periods below 50% charge will drain the 12v battery. They said the 120v charging should only be used in an emergency to get enough charge to reach a 240v or high speed charging station. I can only speculate Porsche is worried about potential issues with extended 120v charging causing problems to the onboard charger in the Taycan since it doesn't matter if I plug it into the appropriate NEMA 15 outlet or hardwire the charger into my electrical system. Either way they say not to charge at 120V for more than 12 hours. I've been fine just keeping it at 50% before I leave it for a week or two and I don't even see a 1% drop in the battery after two weeks so I see no issues.

 

[DMTonka]

I can only comment on question 1. The manual seems very clear about using a trickle charger if in storage for longer than 6 weeks.

Your manual is slightly different from mine. Hard to tell if the information is changing or if it is still a gray area and Porsche's own understanding of best practices are evolving with more real world usage and scenarios...

Oki

 

[Hirschaj]

Your manual is slightly different from mine. Hard to tell if the information is changing or if it is still a gray area and Porsche's own understanding of best practices are evolving with more real world usage and scenarios...

Oki

Your screenshot only applies to the HV battery. My screenshot applies to the 12V battery.

 

[Tooney]

I believe it’s a little unclear in the TSB still; it does not clarify if the 12v is only charged when the car is in drive or also when the vehicle is parked as the HV battery isn’t active?

OP I assume your charger is compatible with lithium ion? My c-tek has a button to reset the battery electronics if a battery state gets to low.

Couple of old posts about process used for charging 12v battery:
https://www.taycanforum.com/forum/threads/dash-cam-and-12v-battery.13972/#post-210566

https://www.taycanforum.com/forum/t...or-service-for-new-battery.14846/#post-224707

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