Larry Cable

Just as an FYI to all those with AG LI batteries installed.

I installed an AG H6 40ah battery in the '18 GT3 back earlier this year, and apart from an initial (post disconnect) startup 'low voltage' transient fault code, I have had no problems since.

I took my car in for its annual 12k ($517) service, which included an oil change and a PCM update AFAIK...

literally as I drove the car off the dealer's lot the following occurred:

- RWS failure
- steering assist failure

I took the car back to the dealership and they attached the PIWIS and cleared the fault codes, dealership claims that the Ag battery is not "entirely compatible" with the 991.2 GT3 electrical systems and the car will continue to throw codes.

I left the dealership and it threw:

- RWS failure
- steering assist failure
- check rear tail light warning
- battery limited operation warning

I checked the AG battery using the BT app - - 97% charged 13.36v ...

stopped for gas - upon restart codes were cleared (apparently)

FYI

DiscoWagon

Our cars are just kind of testy with batteries. This same issue happened to me when I installed an Antigravity battery. Took it to the dealer, they tried to diagnose and said the battery was not compatible. My buddy had the exact same battery (we actually ordered ours together in the same order), we swapped batteries and my car was totally happy with it. Been driving with the other AG battery for over a year with no more fault code issues.

Larry Cable

exactly same spec battery, 40 or 60aH???

TET GT3

But you only had issues after leaving the dealership? Seems strange.

No issues here with my 40ah. I do keep it on the appropriate charger though since it sits for a week or two between drives.

DiscoWagon

In my scenario both batteries were identical, 30Ah.

Larry Cable

yep I keep my 40Ah on the recommended CTEK Li trickle charger...

my guess/theory is that if/when the battery is disconnected and/or an ECU reset occurs the car 'dos not like what it sees' and freaks out - after a while it 'learns' and is copacetic

30Ah wow!

jrbkarter

Certain codes, specifically the RWS and Steering Assist codes can be "cleared" by the dealer PIWIS (factory scan tool) but until the car is driven and the sensors recalibrate, the codes will remain persistent/in the info screen dash. When certain modules are reset (which almost certainly a full reset was performed after the battery swap) they lose their retained data such as max travel for the electronic steering rack travel sensors and the actuators sensors for the rear wheel steering. The modules need to relearn those sensor positions and confirm everything is in spec for the errors to clear on the info screen dash. The relearn is usually quickly achieved during a normal drive or by simply going lock to lock slowly at a stand still or a few low speed circles in a parking lot.

Larry Cable

there was no "battery swap" - I installed the AG months ago - it was a simple oil change and PCM flash AFAIK

but the codes cleared after a short drive as you described

Antigravity

Thanks for the post Larry... I'm am quite experienced with this subject since I changed out batteries in my (now sold) 2016 GT3 RS about 70 to 100 times I figure in all honesty...

As others have stated, and as an FYI for anyone changing a battery... the basics are that the Car will notice it has gone to zero Volts when you change out a battery and in most cases the Car will usually throw flags when you first drive it since the computer saw it completely lost voltage. So upon driving the car a little bit the flags go away as the Car realizes/learns it has proper voltage and sees a battery there. Also sometimes it works good after driving a little bit to turn off the key and take it out, then restart the car, that is called cycling the key and the car then knows it has had a battery in it and the voltage is good so the flags go away. This issue has nothing to do with Lithium or Lead acid...nor does it happen every time from my personal experience with my Car, but in a majority of the times you do a change out it does.

Larry, in your circumstane you did not change out the battery, I understand the dealer just did a few things, but this can also occur with simply disconnecting the Negative Terminal which they might do during a service for safety reason and so nothing is "live" in car as they do the oil change.

Also note that Porsche Dealers will notoriously claim that any aftermarket part in the car than their own Porsche Part is the "Problem", if there is a flag or other issue. I have personal experience with a Porsche Dealers that left a very sour taste in my mouth for the outright false statements they made about batteries in Cars and trying to blame a stuck E-Brake in my RS because the car had our Lithium Battery. Then tried to say it would cost $5k to fix it and the sensor. It was so absurd that I called the GM for the Dealership and said you guys better know about the Magnuson-Moss act and stop telling me falsehoods about electrical systems and batteries in Cars and get the car fixed immediately or this will escalate quickly. They called back the next day and said they were fixing it and sorry for the confusion.

My point is not that all dealers are liars or jerks but rather that they honestly don't know much about the Cars, and the claim they made that a lithium battery is not fully compatible with the Porsche is ignorance of the facts. A car can't tell the difference between the batteries in it, the lithium does not give off some odd voltage or anything, it is simply a battery that sits at 13.2v rather than 12.6v has more power and is lighter weight, it charges perfectly fine with the Cars system just as a lead/Acid battery does. The car just sees the voltage and 13.2v is the same as a lead/acid can have at time also. So the Car won't know any difference. I will say in development we had some flags come up... that was not because the Lithium Battery, but rather because we had a very conservative Battery Management system and the programming was very strick, we easily fixed that and it eliminated the flags.

Also Cars charging system is a standardized system that operates in general the same way in all vehicles be it a boat, car, motorcycle and airplane if they are using a 12v system. They will all operate the same. The only thing different about the batteries is levels of quality, and having a size the fits best for your particular vehicle and its requirements for cranking power and reserve Capacity. But an Auto Battery is simply a larger version of a Motorcycle Battery so you could put that Auto Battery in your motorcycle and it would work fine. I'm rambling about this because some try to make the batteries seem completly different, but they aren't.

Last so everyone understands... a battery does not PUSH energy ever into any part of the car's system or accessories and cannot damage the components. The fact is completing any circuit such as a lightbulb or heated seats in the car only allow that Accessory to PULL the energy is requires from the Battery. So a battery can't fry any part of an electrical system at all, UNLESS you use a 18v battery in a 12v system or do a reverse polarity connection, which you can't do in a Porsche actually, the cable won't reach the terminals if the battery is reversed. Oh, one more thing a lithium battery can only put out it 13.2 nominal voltage and it is the Alternator that charges the Battery above 13.2v, and it is the Alternator that will ever put out more than the 13.2v and go up into the 15v range... the battery cannot do that. So it irritates me when dealers say a battery harmed any part of an electrical system because in fact the electrical system is designed to be able to handle the higher Voltage output that runs the systems, and is specifically put out by the Alternator, not the battery.

Larry Cable

Thanks @Antigravity for this detailed response it is greatly appreciated!

I think I pretty much intuited what you detail above from the behavior of the car after the dealer service and my experience of the initial installation/replacement of the OEM lead acid.

It does appear that the 991.2 is very sensitive to disconnection of battery power supply and will throw a bunch of random and transient fault codes once reconnected ... this is what I experienced after my dealer service.

after driving the car home all the fault cleared and the car is fine, and the battery monitor shows that the AG is happy and healthy...

I guess my takeaway that I would share with others using the Ag in their 991.2's is:

expect some transient fault codes should your dealer disconnect your battery during the service...

expect the dealer to blame the Ag

what's more - it was a little surprising that they let me drive it off the lot throwing those!

I wont be swapping out my Ag any time soon!

p.s your point about the car not being able to tell one battery from another is a good point - electrons are the same coming from Li or Lead/Acid ...