Trickle charging Taycan 12v battery through OBDII port

[Gino]

I have confirmed you can trickle charge the 12v lithium battery through the OBDII port since I was told using the cigarette lighter port could not be used for this purpose like normal ICE Porsche vehicles.

I’m told the fuse on the OBDII 12v connection is 3 or 4 amp but I assume a small trickle charger specifically for lithium ion batteries at 75mA to 1.5mA should be more than enough to insure the 12v lithium battery is properly maintained any time the vehicle is left for a week or more with no use.

I know the main HV battery is supposed to keep the 12v lithium battery charged as long as it is at 50% or greater SOC but I have noticed on this forum that there have been times where the 12V battery has died even though the HV battery was above 50% SOC.

The other option suggested was to leave the frunk released so you can easily get to the battery to put a trickle charger on it if it were to die after being idle for weeks or longer.

This would require having to close the frunk every time which would be more of a pain than simply unplugging the OBDII connector or the SAE pigtail which would connect to the trickle charger at the driver’s side door.
This way, even if the 12v battery were to die you would still have the ability to charge it through the OBDII port.

I’m hoping someone would know what the maximum charge current would be at this port without increasing the fuse rating. Ideally I will only need to trickle charge to maintain the 12v battery but if it were to die I may need more current to be able to operate features in the vehicle or charge the battery quicker.

I drive this vehicle very infrequently since I have 3 other vehicles that get more use. The Taycan will sit for 3 or 4 days a week when I’m in town and can sit for several weeks to a month when I’m traveling so I want to make sure my 12V battery is maintained like all my other vehicles which have trickle chargers on them to insure their starting batteries are always fully charged.

I would appreciate any thoughts or suggestions.

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[Watchesandburgers]

For infrequent use, I would plug the car in to a 110v home outlet. This type of outlet will provide a max charge of about 3 miles an hour. I understand this isn’t exactly what you were asking for, but the main battery should keep the 12v battery charged. Using a standard 110v outlet will ensure a minimum of electrical draw over time. Hope that helps.

 

[Gino]

For infrequent use, I would plug the car in to a 110v home outlet. This type of outlet will provide a max charge of about 3 miles an hour. I understand this isn’t exactly what you were asking for, but the main battery should keep the 12v battery charged. Using a standard 110v outlet will ensure a minimum of electrical draw over time. Hope that helps.

Unfortunately there is a Porsche service bulletin which states clearly you should never charge at 120V for more than 12 hours only in an emergency.
I would have to put the Porsche charger on a timer so it will only charge for 8 hours each night which could be a good solution. I’ll have to check into what timers I can use which will allow me to turn the 120V charger off after 8 hours each day when I’m gone.
I was told by my service advisor that I can’t set the 120V charger to start & stop charging. I don’t have 220V in my garage yet otherwise I would simply leave it plugged in and charge the vehicle whenever the SOC dropped to 50% SOC and stop it once it reached 85% SOC.
Thanks for giving me another idea to accomplish my goal to maintain my 12V battery with my existing charging cables…

 

[Gino]

Unfortunately there is a Porsche service bulletin which states clearly you should never charge at 120V for more than 12 hours only in an emergency.
I would have to put the Porsche charger on a timer so it will only charge for 8 hours each night which could be a good solution. I’ll have to check into what timers I can use which will allow me to turn the 120V charger off after 8 hours each day when I’m gone.
I was told by my service advisor that I can’t set the 120V charger to start & stop charging. I don’t have 220V in my garage yet otherwise I would simply leave it plugged in and charge the vehicle whenever the SOC dropped to 50% SOC and stop it once it reached 85% SOC.
Thanks for giving me another idea to accomplish my goal to maintain my 12V battery with my existing charging cables…

Spoke to my Porsche service advisor yesterday and he suggested to simply use the 120v Porsche charger plugged into a timer so that I can charge for a hour or two at most each day to maintain the 12V battery as a backup from the normal operation where the 12V battery is kept charged as long as you have 50% SOC or more while in storage. He said 1 or 2 hours is more than enough to achieve this task and it stays away from the strong suggestion by Porsche not to charge for more than 12 hours except in emergencies regardless if Porsche is concerned their charger or the charging system will fail with prolonged use or the customers wiring/outlet is improperly sized to allow for extended charging sessions. He said it is more likely Porsche does not want to tax their mobile charger or the charging system in the vehicle since it goes without saying that my local dealer sends out a licensed electrician to verify the customer’s set up in their garage.
Also he said it is up to the customer to insure when traveling that they should insure wherever they decide to plug into a 120V outlet that they refrain from charging more than 12 hours because the outlet may not be properly sized and lead to overheating of the outlet/plug and cause damage which would not be the responsibility of Porsche.
So there is no need to charge through the OBDII port as long as I add a 15A mechanical timer to my 120V charger to charge for an hour or two a night when I’m away.

 

[Watchesandburgers]

Gino, this all seems irrelevant to me. You shouldn't need to purchase a mechanical timer or any kind of ODBC charger. This can all be accomplished in-car using the Timer and Profile settings. Here's my suggestion.

1. For the Timer, which you should already have set, it should look like this: Ready for departure at 7:00 AM (or similar). Every day of the week selected. Target charging 85%. This is the maximum charge value for any L1/L2 charge session.
2. For the Profile, you should already have one called "Home". It should be set with your home address and a minimum charge value of 25%. You can increase this to 50% if you want. Set the Preferred Charge Period to overnight, 10:00 PM - 4:00 AM or similar.

This will set the car to immediately charge up to the minimum number (25% or 50%) between 10 PM - 4 AM. From there, it will continue to charge up to 85% each night between those hours. When it reaches 85% it will only charge when necessary. The car may only lose 1-2 miles of range a day, so the car will stay at 85%. This is equivalent to a trickle charger for an ICE car.

From an 11-year Tesla owner, believe me when I say, a plugged in EV is a happy EV. Enjoy!

 

[Gino]

Gino, this all seems irrelevant to me. You shouldn't need to purchase a mechanical timer or any kind of ODBC charger. This can all be accomplished in-car using the Timer and Profile settings. Here's my suggestion.

1. For the Timer, which you should already have set, it should look like this: Ready for departure at 7:00 AM (or similar). Every day of the week selected. Target charging 85%. This is the maximum charge value for any L1/L2 charge session.
2. For the Profile, you should already have one called "Home". It should be set with your home address and a minimum charge value of 25%. You can increase this to 50% if you want. Set the Preferred Charge Period to overnight, 10:00 PM - 4:00 AM or similar.

This will set the car to immediately charge up to the minimum number (25% or 50%) between 10 PM - 4 AM. From there, it will continue to charge up to 85% each night between those hours. When it reaches 85% it will only charge when necessary. The car may only lose 1-2 miles of range a day, so the car will stay at 85%. This is equivalent to a trickle charger for an ICE car.

From an 11-year Tesla owner, believe me when I say, a plugged in EV is a happy EV. Enjoy!

Thanks! I had set my home & away settings to 85% it didn’t work when it was at the Porsche dealer. They always gave it back to me at 100% even though the setting was at 85%.
I’m going to try to use the vehicle timer again to stop at 85% to see if that works. If it does then I’m home free…

 

[Watchesandburgers]

The trick is to set both a profile and a timer. It’s decidedly unintuitive. ?

 

[satchurator]

The trick is to set both a profile and a timer. It’s decidedly unintuitive. ?

@Watchesandburgers But he's on L1. If he rolls in at 10% SOC, with both profile and timer set, the car would still immediately seek to charge to the minimum of 25% which at ~1.2kW would take over 12 hours.
And then, as you state - the preferred charging time is just a preference. For an 85% min target, the car won't have reached that and will just keep chugging.
In summary, unfortunately I don't think a profile plus timer will give @Gino what he needs at L1.

 

[Botox]

I went through everything trying to keep my 2020 Taycan turbo S 12v battery charged as I leave the car at my second home, sometime don’t drive it for 1-2 months. Trickle charging 12v didn’t work, leaving it plugged in, etc… Eventually my car went thru extensive battery inspection and repair of the main battery about 1 year ago, long before the battery recall, so now I charge to 70-80 percent before leaving, unplug from 220V wall charger, and leave it, turn off motion sensors. The big battery should forever keep the little battery charged, and there is minimal vampire drain of only 1-3 percent per 1 month time. before battery repair, nothing worked. Also, You can periodically precondition car remotely for the phone app which will wake car up and start the charging of the 12v if the large battery is failing to do so.

 

[Gino]

For infrequent use, I would plug the car in to a 110v home outlet. This type of outlet will provide a max charge of about 3 miles an hour. I understand this isn’t exactly what you were asking for, but the main battery should keep the 12v battery charged. Using a standard 110v outlet will ensure a minimum of electrical draw over time. Hope that helps.

It appears that is my best option…
Thanks

@Watchesandburgers But he's on L1. If he rolls in at 10% SOC, with both profile and timer set, the car would still immediately seek to charge to the minimum of 25% which at ~1.2kW would take over 12 hours.
And then, as you state - the preferred charging time is just a preference. For an 85% min target, the car won't have reached that and will just keep chugging.
In summary, unfortunately I don't think a profile plus timer will give @Gino what he needs at L1.

I always leave the car at greater than 50% when I’ll be gone for a week ir more so maybe I can figure out how long it takes to get from a certain SOC above 50% which would get me to 85% or charge to 85% before I leave and let my L1 charger keep it there while I’m gone. I just don’t want it maintaining SOC at 100% in my garage for any extended timeframe since Porsche warns not to charge to 100% too often which appears to degrade the battery over time and increase risk of fire…

 

[Gino]

I went through everything trying to keep my 2020 Taycan turbo S 12v battery charged as I leave the car at my second home, sometime don’t drive it for 1-2 months. Trickle charging 12v didn’t work, leaving it plugged in, etc… Eventually my car went thru extensive battery inspection and repair of the main battery about 1 year ago, long before the battery recall, so now I charge to 70-80 percent before leaving, unplug from 220V wall charger, and leave it, turn off motion sensors. The big battery should forever keep the little battery charged, and there is minimal vampire drain of only 1-3 percent per 1 month time. before battery repair, nothing worked. Also, You can periodically precondition car remotely for the phone app which will wake car up and start the charging of the 12v if the large battery is failing to do so.

That’s what I’m thinking will be the best option for me too. If I charge it to 85% and leave it unplugged I should never have any issue unless something fails while I’m gone.
Anything that fails would be under warranty until 2030 for the car, the 12V battery system or the main battery.
Hopefully by then I will have more confidence in the reliability of my 2021 Taycan in general which would allow me to hang onto my baby…
Thanks for all the comments & solid advice.

 

[wmras]

Also, You can periodically precondition car remotely for the phone app which will wake car up and start the charging of the 12v if the large battery is failing to do so.

After 4 years and 22,000 miles in our 2020 Taycan Turbo S, I confirm this has always worked for us - have never had a 12V battery failure. It has been left disconnected up to three months.

And am never in a hurry to plug it in unless the HV battery is less than 50% or we plan a trip the next morning.

 

[Gino]

After 4 years and 22,000 miles in our 2020 Taycan Turbo S, I confirm this has always worked for us - have never had a 12V battery failure. It has been left disconnected up to three months.

And am never in a hurry to plug it in unless the HV battery is less than 50% or we plan a trip the next morning.

That does sound like the best plan for me. It is easy for me to plan ahead to charge the vehicle to 60% or more before I leave the car for weeks or months to insure the 12V battery is properly maintained. I don’t see more than a loss of 1 or 2 miles in range after each week in storage which is likely due to me or my wife checking the charge status on the vehicle each day which wakes up the car.
In your experience, if I forget & leave it with less than 50% on a rare occasion would preconditioning through the app also charge the 12V battery or would I just need to resist opening the app while I’m gone to avoid waking up the car too often and drain the 12v battery?
I have yet to leave the car with less than 50% SOC once I was told to do so and have had no issues.
One thing I have noticed is that the display on the dash always shows 13.2 to 13.5 volts whenever I turn on the vehicle which shows me the main battery is charging the 12V battery which is likely at 12 to 12.8 volts when it is not being charged if it’s like a normal 12V battery. This appears to confirm your logic that just waking the car up should initiate charging of the 12V battery unless it only kicks in once the voltage drops to a certain level below 12.8V. Worst case setting the battery to precondition for a charge should force it to check/maintain the 12V battery…
Thanks so much. I think this is the best way for me to proceed and not worry about trickle charging at all. Then I can only use the L1 charger in emergencies as Porsche strongly suggests.

 

[Vercingetorix]

That does sound like the best plan for me. It is easy for me to plan ahead to charge the vehicle to 60% or more before I leave the car for weeks or months to insure the 12V battery is properly maintained. I don’t see more than a loss of 1 or 2 miles in range after each week in storage which is likely due to me or my wife checking the charge status on the vehicle each day which wakes up the car.
In your experience, if I forget & leave it with less than 50% on a rare occasion would preconditioning through the app also charge the 12V battery or would I just need to resist opening the app while I’m gone to avoid waking up the car too often and drain the 12v battery?
I have yet to leave the car with less than 50% SOC once I was told to do so and have had no issues.
One thing I have noticed is that the display on the dash always shows 13.2 to 13.5 volts whenever I turn on the vehicle which shows me the main battery is charging the 12V battery which is likely at 12 to 12.8 volts when it is not being charged if it’s like a normal 12V battery. This appears to confirm your logic that just waking the car up should initiate charging of the 12V battery unless it only kicks in once the voltage drops to a certain level below 12.8V. Worst case setting the battery to precondition for a charge should force it to check/maintain the 12V battery…
Thanks so much. I think this is the best way for me to proceed and not worry about trickle charging at all. Then I can only use the L1 charger in emergencies as Porsche strongly suggests.

Taycan has a Lithium battery. 13.3 volts is normal for them.

 

[wmras]

In your experience, if I forget & leave it with less than 50% on a rare occasion would preconditioning through the app also charge the 12V battery or would I just need to resist opening the app while I’m gone to avoid waking up the car too often and drain the 12v battery?

I have yet to leave the car with less than 50% SOC once I was told to do so and have had no issues.

One thing I have noticed is that the display on the dash always shows 13.2 to 13.5 volts whenever I turn on the vehicle which shows me the main battery is charging the 12V battery which is likely at 12 to 12.8 volts when it is not being charged if it’s like a normal 12V battery.

Porsche has recommended 40-50% charge for long-term storage or trips to Service. We have left our 2020 TS set disconnected for days down to 40% with no issues. Connecting via phone app more than once a day might make you feel better but is not necessary.

From batteryworld.com.au :
"A 12v lithium LiFePO4 battery fully charged to 100% will hold voltage around 13.3-13.4v. Its lead acid equivalent will be approximately 12.6-12.7v."

All our Porsche vehicles with LiFePO4 batteries are always >13 volts and charge near 13.8v.

We drive our 2020 TS like any other Porsche, do not baby it, do not always connect it, but always lock it when parked, even in our garage, and we make sure the keys are far from the car. Works like a dream for trouble-free driving.

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