Problems with trickle charging 12 volt battery

[Kinney]

I plugged a CTEK MXS 5.0 battery tender into the 12 volt outlet in the console of my 2021 Taycan 4S. The power lamp on the CTEK indicated that it was not connected and therefore not charging. I then plugged the CTEK into the 12 volt outlet in the trunk of the car. Again, the power lamp on the CTEK indicated that it was not connected and therefore not charging. I did the same thing with another CTEK MXS 5.0. It also indicated that it was not connected and therefore not charging. Both of the CTEK tenders work properly when I plug them into two 911 Porsches. Can anyone tell me why I am having trouble using the CTEK with the Taycan?

Thank you for any guidance you might provide me.

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[daveo4EV]

the Taycan is not an ICE car - the electrics are very different - trickle charging the 12V should not be necessary - the big battery will charge it - the 12V is also a LiON battery which has different depletion while idle characteristics - I wouldn’t be surprised if the 12V outlets are all off line when the car is “off”

if you want to try and charge the 12V you‘ll probably have to attach the charger to the 12V jumper posts under the frunk hood…

 

[Vercingetorix]

That charger isnt made for lithium batteries. You want the Litium US for a lithium battery.
https://smartercharger.com/collections/all/products/ctek-lithium-us

 

[Mike in CA]

Both @daveo4EV and @Vercingetorix are correct. First you'll need a charger/maintainer for a lithium, not a lead acid, battery and you'll need to connect it to the under-frunk terminal posts. Instructions on how to do this on the 2021 4S can be found under "12V Battery" on page 270 in the owners manual.

 

[Kinney]

That charger isnt made for lithium batteries. You want the Litium US for a lithium battery.
https://smartercharger.com/collections/all/products/ctek-lithium-us

 

[Kinney]

Thank you, everyone, for the information about using a CTEK MSX 50 to maintain the 12-volt battery in my Taycan 4S. This is what I now understand:

• A CTEK MSX 5.0 battery tender is not suitable for the 12-volt ion battery in the Taycan. A CTEK Lithium US battery tender must be used.
• The 12-volt outlets in the Taycan's console and in its trunk are turned off when the car is turned off. A CTEK Lithium US tender would have to be connected to the appropriate terminals in the frunk.
• The High-Voltage traction battery that drives the car is designed to maintain the 12-volt battery for long periods of nonuse. A trickle charger, therefore, is not necessary.
• There are contradictory technical bulletins about keeping the Mobile Charge Connect to the car for long periods. One recommends to do so; the other recommends not to do so because the Mobile Charge Connect could drain the 12-volt battery.
• If it is not clear that keeping the Mobile Charge Connect is good or bad for the 12-volt battery, it seems to me that it might be wise to use the CTEK Lithium US battery tender, connected to the terminals in the frunk.

Is my understanding correct?

 

[Vercingetorix]

Thank you, everyone, for the information about using a CTEK MSX 50 to maintain the 12-volt battery in my Taycan 4S. This is what I now understand:

• A CTEK MSX 5.0 battery tender is not suitable for the 12-volt ion battery in the Taycan. A CTEK Lithium US battery tender must be used.
• The 12-volt outlets in the Taycan's console and in its trunk are turned off when the car is turned off. A CTEK Lithium US tender would have to be connected to the appropriate terminals in the frunk.
• The High-Voltage traction battery that drives the car is designed to maintain the 12-volt battery for long periods of nonuse. A trickle charger, therefore, is not necessary.
• There are contradictory technical bulletins about keeping the Mobile Charge Connect to the car for long periods. One recommends to do so; the other recommends not to do so because the Mobile Charge Connect could drain the 12-volt battery.
• If it is not clear that keeping the Mobile Charge Connect is good or bad for the 12-volt battery, it seems to me that it might be wise to use the CTEK Lithium US battery tender, connected to the terminals in the frunk.

Is my understanding correct?

I’m pretty sure the Noco chargers can also be used. They all seem lithium compatible. The 1 amp version is like $30.

 

[Mike in CA]

Thank you, everyone, for the information about using a CTEK MSX 50 to maintain the 12-volt battery in my Taycan 4S. This is what I now understand:

• A CTEK MSX 5.0 battery tender is not suitable for the 12-volt ion battery in the Taycan. A CTEK Lithium US battery tender must be used.
• The 12-volt outlets in the Taycan's console and in its trunk are turned off when the car is turned off. A CTEK Lithium US tender would have to be connected to the appropriate terminals in the frunk.
• The High-Voltage traction battery that drives the car is designed to maintain the 12-volt battery for long periods of nonuse. A trickle charger, therefore, is not necessary.
• There are contradictory technical bulletins about keeping the Mobile Charge Connect to the car for long periods. One recommends to do so; the other recommends not to do so because the Mobile Charge Connect could drain the 12-volt battery.
• If it is not clear that keeping the Mobile Charge Connect is good or bad for the 12-volt battery, it seems to me that it might be wise to use the CTEK Lithium US battery tender, connected to the terminals in the frunk.

Is my understanding correct?

Your understanding on the first two bullet points is correct, although I'm sure there are other chargers besides CTEK which are lithium compatible. CTEK just makes a quality unit.

Someone please correct me if I'm wrong, but I believe the High-Voltage traction battery only charges the 12V battery when the vehicle is being operated, not when it's sitting idle. If you don't drive the car for extended periods of time I think using a battery maintainer periodically is a good idea.

That said, I do not leave the tender hooked up to the 12V lithium battery all the time. If I haven't been driving the car for a while I will occasionally hook up the the CTEK unit until it completes it's charging cycle. Since lithium batteries last longer if they are not constantly held at full charge I then disconnect it.

As for keeping the main battery connected to the PMC/PMCC is concerned, as you mention there are mixed signals about that. Personally, I see no reason to keep the car plugged in after a charging session and I always disconnect there as well.

 

[daveo4EV]

just because you're plugged in doesn't mean you're charging the battery - the on board charger starts/stops AC power flow when it deems it necessary - if the car is not charging and it's plugged in it's no different that being un plugged (this can be confirmed by the PMCC unit showing no power flowing) - the only difference is the car can "top" itself off if it needs to but I'm unaware of any circumstance under which the Taycan would do that…

that being said Porsche recommends I believe in 'good to know' that you leave the car unplugged if you're not using it for a while - there is virtually no draw on the 12V when teh car is off, and the car can "wake up" the big battery to charge the little battery if it detects the 12V is low…

EV's behave very differently from ICE's in how they interact with the 12V batteries…

a better option and more generically useful is a LiON battery jumpstarted - because it can "start" the Taycan if the 12V is dead - where as the power flow from a 12V trickled charger will NEVER charge the 12V once it's dead/tripped-offline because it's behind a relay

once the Taycan's 12V is dead the _ONLY_ way to wake it up is via a 12V booster battery which provides a enough power to boost-wake the main computer which will then trip the 12V relay to close (power flow) and then wake up the big battery to begin charging the 12V battery - a 12V cTek charger does not provide enough power to boot-strap the main car CPU to begin the vehicle recovery process…

in addition to being able to walkup the Taycan form fully dead (which a trickle charger will NEVER do due to the 12V relay) - battery boosters also tend to provide:

• jump start ICE
• jump start EV
• USB charging ports
• flash light capability

I'm very very dubious of the value of 12V trickle charger in the context of any EV - and in particular the Taycan - LiON batteries don't "lose" charge while sitting there, and the Taycan uses virtually no power from the 12V if it's off…

also _IF_ there is a draw history has demonstrated that the trickle chargers can't keep up with any actual draw the Taycan has on the 12V and the 12V has so little capacity the Taycan can out-power a trickle charger and will deplete to the battery low enough to trip the relay in any cash…

so the scenior is as follows:

• if there is no actual draw - there is no need for the trickle charger
• if there is a draw - it will be more than the tickle charge can replace so battery will go dead anyways
• the car will wake up the big battery to charge the 12V if necessary even when the car is "off"
• once the 12V battery is dead/off-line the trickle charger doesn't provide enough power to wake the car up again and the 12V battery is "off line" so it can't be charged until the mail computer trip's it's relay…

 

[Mike in CA]

just because you're plugged in doesn't mean you're charging the battery - the on board charger starts/stops AC power flow when it deems it necessary - if the car is not charging and it's plugged in it's no different that being un plugged (this can be confirmed by the PMCC unit showing no power flowing) - the only difference is the car can "top" itself off if it needs to but I'm unaware of any circumstance under which the Taycan would do that…

I realize the main battery isn't charging just because it's plugged in. I also see no point in keeping it plugged in which is why I don't.

that being said Porsche recommends I believe in 'good to know' that you leave the car unplugged if you're not using it for a while - there is virtually no draw on the 12V when teh car is off, and the car can "wake up" the big battery to charge the little battery if it detects the 12V is low…

How is the alarm system powered? When accessing the vehicle via the Porsche Connect app what powers the monitoring functions? If one is in and out of the car for various reasons, with operation of the door handles, interior lights, audio system etc, aren't these functions powered by the 12 V battery? Also, do you have a link to the source which describes the threshold at which the main battery wakes up to charge the 12V battery? I'd be interested to read about that.

EV's behave very differently from ICE's in how they interact with the 12V batteries…

a better option and more generically useful is a LiON battery jumpstarted - because it can "start" the Taycan if the 12V is dead - where as the power flow from a 12V trickled charger will NEVER charge the 12V once it's dead/tripped-offline because it's behind a relay

once the Taycan's 12V is dead the _ONLY_ way to wake it up is via a 12V booster battery which provides a enough power to boost-wake the main computer which will then trip the 12V relay to close (power flow) and then wake up the big battery to begin charging the 12V battery - a 12V cTek charger does not provide enough power to boot-strap the main car CPU to begin the vehicle recovery process…

in addition to being able to walkup the Taycan form fully dead (which a trickle charger will NEVER do due to the 12V relay) - battery boosters also tend to provide:

• jump start ICE
• jump start EV
• USB charging ports
• flash light capability

I'm very very dubious of the value of 12V trickle charger in the context of any EV - and in particular the Taycan - LiON batteries don't "lose" charge while sitting there, and the Taycan uses virtually no power from the 12V if it's off…

That's interesting in the context of the behavior of my CTEK lithium charger. The CTEK Lithium US has an 8 step charging program. Step 2 is a bulk charging mode which will charge until the battery is at 90% at which point it switches to step 3 (absorption mode) which takes the charge to 95%. After an analysis mode, the charge is maximized at 100% followed by a float mode. I've noticed that, depending on how long it's been since the car was driven or the last charging session occurred, the amount of time it takes for the charger to complete the mode cycle and arrive at float mode can vary by several hours. If the 12V battery doesn't discharge from a load over time I would have expected approximately the same brief charging behavior every time I hooked it up, regardless of how long the battery has just been sitting there.

Also, with regard to being able to boost-wake the main computer, do you know how much current is required? I have a different CTEK unit with a "Supply mode" which can provide a constant voltage of 13,6V and up to 7A of current. Would this be sufficient?

also _IF_ there is a draw history has demonstrated that the trickle chargers can't keep up with any actual draw the Taycan has on the 12V and the 12V has so little capacity the Taycan can out-power a trickle charger and will deplete to the battery low enough to trip the relay in any cash…

The CTEK Lithium provides up to 4.3 amps of current in bulk mode which seems pretty healthy considering the normal demands on the 12V battery. If the nominal draw on the 12V battery when idle is greater than can be addressed by that ( I thought it had almost no draw on it?) there is probably something wrong.

Also, I guess the question has to be asked, if charging maintenance of the 12V battery is completely unnecessary why does Porsche bother to include a multi-page description of how to do it in the owner's manual? Seems like it would be easier to just say: Charging 12V battery; not required.

Anyway, thanks for the feed back and the discussion.

 

[daveo4EV]

the Taycan has to charge the 12V while it's "off" using the big battery - cause the amount of power in the 12V just isn't that great - and the alarm and other components would drain it in a matter of a couple of days - the 12V replacement battery is more like a motorcycle/ATV battery than a normal automotive battery in terms of capacity…

as to why Porsche documented how to trickle charge it - well I'd suggest there is simple reason - it was already written for all their other vehicles and it was simply cut/paste - cause corporations don't give that a lot of thought and the doc's people probably weren't given instructions to give it any deep thought…and it doesn't hurt.

People have left their Taycan's unplugged and off for months at this point in time and the 12V is alive/well with no trickle charger - there is just no way the Taycan would last a week or two unplugged from charging for the 12V given it's capacity unless the big battery kicks in occasionally and charges the 12V…

 

[Mike in CA]

the Taycan has to charge the 12V while it's "off" using the big battery - cause the amount of power in the 12V just isn't that great - and the alarm and other components would drain it in a matter of a couple of days - the 12V replacement battery is more like a motorcycle/ATV battery than a normal automotive battery in terms of capacity…

as to why Porsche documented how to trickle charge it - well I'd suggest there is simple reason - it was already written for all their other vehicles and it was simply cut/paste - cause corporations don't give that a lot of thought and the doc's people probably weren't given instructions to give it any deep thought…and it doesn't hurt.

People have left their Taycan's unplugged and off for months at this point in time and the 12V is alive/well with no trickle charger - there is just no way the Taycan would last a week or two unplugged from charging for the 12V given it's capacity unless the big battery kicks in occasionally and charges the 12V…

I'm not sure about the cut and paste explanation. AFAIK, the Taycan is the only current Porsche that comes standard with a lithium 12V battery and the instructions in the Taycan manual are lengthy, quite specific to lithium, and share little in common with the battery info in the manuals for my previous 3 Porsches (991.1 GT3, Cayenne, 997.2).

The manual does state that charging with an appropriate LiFePO4 approved charger for at least 10 minutes will re-awaken the electrical system after a low 12V battery situation, although given the main battery supposedly charges the 12V battery when idle (would still love to see documentation on that) this should be an extremely rare occurrence . If nothing else, having a charger will be useful in the event of a problem.

 

[Scandinavian]

once the Taycan's 12V is dead the _ONLY_ way to wake it up is via a 12V booster battery which provides a enough power to boost-wake the main computer which will then trip the 12V relay to close (power flow) and then wake up the big battery to begin charging the 12V battery - a 12V cTek charger does not provide enough power to boot-strap the main car CPU to begin the vehicle recovery process…

Interesting discussion on the benefits of a Lithium trickle charger. I use one if I leave the car for a few months in the garage, if needed or not is another question.

The Taycan certainly draws very little power from the main battery when left for a long time. I think I have seen a percentage or two when left for 9 weeks?

Just to add to the discussion on whether the CTEK can help out when the 12 volt battery protective relay has disconnected the 12 volt battery. The CTEK has a feature that seems to boost the voltage to address this issue, at least here in Europe. Here is a copy from the CTEK manual.

I have never tried to actually Use this feature though, so can not comment on this feature.

 

[ciaranob]

Thought I'd share despite not really pertinent to this specific discussion - my 2015 BMW M4 has a Li Ion battery (full automotive) and I've used the CTek to trickle charge but TBH have never actually needed to do this despite some occasions with car parked fro nearly a month - I got the charger simply as a failsafe. Again much larger battery I assume than in the Taycan so not pertinent to this discussion but in case some are not aware, some ICE cars do have Lithium batteries too

 

[Mike in CA]

Interesting discussion on the benefits of a Lithium trickle charger. I use one if I leave the car for a few months in the garage, if needed or not is another question.

The Taycan certainly draws very little power from the main battery when left for a long time. I think I have seen a percentage or two when left for 9 weeks?

Just to add to the discussion on whether the CTEK can help out when the 12 volt battery protective relay has disconnected the 12 volt battery. The CTEK has a feature that seems to boost the voltage to address this issue, at least here in Europe. Here is a copy from the CTEK manual.

I have never tried to actually Use this feature though, so can not comment on this feature.

The same information also appears in the US manual. Honestly, I had just skimmed over those particular instructions prior to this discussion and your post prompted me to go back to the manual for a closer look. Seems like this could be a useful feature. Thanks for your post!