In fact, I would like to purchase the most suitable AGM battery for the accessory battery and prevent discharge. Would I accept service? If so, I would do that too. After all, the vehicle has a warranty.
If the auxiliary battery capacitor is not charged, the fault is always there. Efb battery can’t support it. Strong agm required
“Love my car” , mmm not so sure I do. 
in fact after all the hassle i’ve had I’m starting to hate the bloody thing 
So what issues are you seeing if your main battery is discharging ?
I’m seeing the Welcome lights & keyless entry not functioning each time.
I also have a message pop up saying that the car is going into"Economy Power Mode", if I leave the ignition on for around 5 minutes.
The manual says these issues will occur if the battery is low, thats why I think my battery is discharging.
I’m not seeing any other issues.
Each time the car goes to the dealership they show me a report saying the batteries are fine ??
I’m struggling to believe that DS have messed up by putting two different battery types in their cars that are not compatible with each other ?
If that is the case why is it only effecting one or two cars ?
I’ve been trying to find out why my car is playing up for 3 months and it’s only yourself that seems to be having a similar issue as me.
If its a manufacturing fault surely there would be information online with many many owners reporting battery faults ?
There would be a mass re-call, but I cant find any other reports of battery issues on any DS model ?
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My previous Volvo had an acid wet main battery (EFB) and a dry start/stop (AGM) supporting battery.
I had that car for 9 years without needing to change any of the batteries.
I did have to charge the main battery now and then, but that was because the car only did 45 miles per week on short journeys and was parked up all weekend.
After a recharge I would reset the BMS.
Do you think there’s a possibility that terms and phrases might be getting lost in translation ?
ecu-ECM for instance could be what our technicians refer to as BMS ?
Just a thought ?
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The service has returned. The engine battery and the rear battery needed to be replaced. He said the auxiliary battery was also faulty. It will be brought from France within 4 weeks. Actually, they can replace the main battery and send it back, but I was surprised that they tested it, congratulations ds. My vehicle is manufactured in 2023, I bought my vehicle in 2024, could it be because you are waiting? I am thinking of going to the service tomorrow, I will get information about the small battery in the back from the technician. 
What is the BMS reset process and how is it done? Did the authorized service recommend this?
For what it`s worth, being a DS4 etense and not a DS7 
I have had “electric drivetrain error” for a couple of weeks, workshop didnt have any possibility to look at the car during christmas holidays.
Left the car this morning and got a call from them at 1100, three hours later 
They have already ordered a sparepart, he spoke something about a connector to the 12V battery that might cause my issue. Will be delivered tomorrow.
At the same time they will change 12V battery as they suspect it might have something to do with the error code…
When they have changed the connector and battery they will continue faultsearching.
What I want to say with this post is that you guys might be right, the 12V battery being bad can certainly give some strange faults that at a first glance shouldnt have anything to do with the 12V battery.
My car is also 2023 bought 2024.
Like your car it was probably sitting in compound for many months.
Not sure on the DS.
But on my Volvo it was easy once you knew how.
It was basically, putting foot on clutch, then turning on ignition, press the rear fog light switch on/off 5 times, the battery icon would then flash 3 times on the dash indicating the BMS had been reset.
I’ve not seen “electric drivetrain error” on my car YET !!!
I do see " system shutting down in electric economy mode", if I leave the radio on for around 5 minutes with no engine running .
I’m also having issues with the welcome lights and keyless entry going into hibernation mode prematurely.
Thats why I think theres an issue with the auxiliary battery.
I’m currently waiting for the technician from Stellantis who last checked my car to update my dealership with a possible cause.
So far they’ve checked all batteries over 48 hrs and found no faults.
They then got DS Technical Headquarters involved who advised to change a control module which had to be ordered from France, this made no difference.
They’ve also done a few updates, which also made no difference.
So now its down to whatever France say. ???
I still think the 12v auxiliary battery or batteries has something to do with it all ?
Fiamm btx14 battery
https://adgdalys.lt/en/product/48165473541/
They delivered my DS vehicle after 3 days. It was concluded that the problem was in the Fiamm btx14 battery, which is the accessory battery at the back. And this battery was ordered from France. It’s very strange how 14 amp is possible. Battery 62 amp. It drains the battery. Two batteries will be replaced. The technician stated that the vehicle is powered from the engine battery for charging in sleep mode. “This feeds the electrical propulsion system,” he said. It was said that batteries would arrive after 1 month.
As I said from the beginning, it’s a labor dispute. Rear battery agm, front main battery efb. And it gets its power from the EFB battery. In my opinion, improvements can be made by updating the operating system, i.e. software. Or both batteries must be in the same class. AGM batteries require strong charging like gel batteries, I have always said this, they are not compatible with liquid batteries. It should not be forgotten that AGM batteries cannot be exposed to heat, insulation is important. EFB batteries cannot power AGM due to loss of performance in cold weather…
I may be wrong, but i believe the AGM can take higher start current but they don`t demand it.
I also thought that it was as good as EFB , having a best operating temp at appr. 25 degree C
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So are they replacing both batteries like for like, ie : one AGM in the rear and one EFB at the front ?
Or putting two AGM ?
Would think that putting AGM in front needs a lot of software adaption due to different caracteristics than EFB
My battery was changed - 260cca instead of 760cca on the old (cold cranking amps).
In accordance to a service bulletin “connector 1” was also replaced.
This cured “electric drive train error”.
But my screens went black as soon as I started the car outside workshop. It was during lunchtime = no techs in the building. Got it documented end gave it a “reboot” disconnecting both batteries.
My thoughts as well.
I just cannot believe that DS have mix matched the batteries.
Surely there would be countless cars going faulty if the main battery should be AGM to match the support battery.
When I stopped at the traffic lights in the city center today, passersby were stuffing their noses. When I parked, an incredible smell came from behind me. The main battery in the front literally gave off a smell of steam. It smelled like rotten eggs. I reported the situation to the service and stated that I would not use the vehicle and that I had to return it with a tow truck. They took delivery and said that the batteries had arrived and that they could be replaced by the end of the week. When I turned on the heating, all the gas filled the passenger compartment. I felt the very dangerous hydrogen gas in the battery inside the vehicle. I survived cheaply…
