Took my 2020 DS7 ETense 300 4x4 hybrid in for the recall check on the traction battery and for general annual maintenance. Apparently only the software needed to be updated for the recall but the dealer says there is an error code indicating the “secondary” battery has a problem and needs to be replaced at a cost of €200 (plus tax), which is not covered under warranty. He says this error appears when the car is started. Has anybody else had this problem? Could the software update have something to do with it? By the way, I am in Portugal.
If the battery is 3-4 years old, it probably needs to be replaced. You can try charging it. It might improve the situation temporarily. This has nothing to do with the software update. It’s a coincidence. In the future, charge it once every month or two.
What do you mean charge it? By running the car or by taking it out and plugging it into a charger?
Check the manual, where it says that the 12V battery can be charged when it is connected to the car (both).
Replacing of AUX 12 V battery is one of maintenance steps. It is normal. But price you mentioned is quite high if we are talking about that small one in rear cargo area.
The purchase and replacement service can cost a lot, especially since it’s an AGM.
Look out for any AGM 12 or 13Ah 200A or by the number 9828201580.
Manual only talks about charging the front battery. Do you mean that charging the front battery also charges the one in the back?
I recently bought a Ring trickle charger. I have it connected straight to the battery and I plan on plugging it in overnight once a month. I’ve only usedit once so far. This should keep the battery in good health without too much sulphate build up.
As a bonus, I have driven about 100 miles so far on full electric only since this first overnight charge, without the ICE starting. My car was built in Sept 2022, so battery is effectively over 3 years old.
From what I’ve read, no alternator can fully charge a battery, typically 80-90%, if it did then there is a possibility it could over charge it and cause a fire, so manufacturers restrict the alternator output. Using a trickle charger will safely charge the 12volt battery to 100%.
Charging the front battery doesn’t charge the rear battery because they’re separate. Therefore, the rear battery must also be charged.
Having had the smaller 12v battery changed twice and the main 12v battery changed 4 times under warranty in just 12 months I still find this subject such a grey area.
I was told by the tech guy at my dealership and by DS UK Technical Dept, on my DS4 E Tense, the smaller 12v battery receives some charge via the main 12v battery, as it’s a one way open circuit, ie charge flows to the smaller battery from the bigger battery but not the other way round.
However, I was also told by another DS tech guy at the same dealership “it wouldn’t be a bad idea to charge the smaller one every so often to keep it topped up because the charge it receives is only a small amount of charge from the main 12v battery”
They also said the main 12v receives some charge from the main traction battery whilst its being charged, with the majority of the charge coming from the alternator via the ICE when it starts up.
Apparently some of that charge also flows through the main 12v battery to the smaller 12v battery ?
If I’m honest though, I’m still unsure how this system works, and I’m not really confident that my dealership service department know either.
On the advice of one of the Tech guys I did buy a CTEK charger which came with quick connect cables that I connected direct to the main 12v battery , (positive to live on the battery & negative to the earth point on the body of the car), ready to trickle charge now & then, but when the service department saw these cables connected to the main battery they tried saying due to the way the system works these cables could be messing with the BMS, which could possibly either be giving false information when they were checking the batteries, or at worse actually draining the 12v batteries, so they asked that I remove them ?
So basically , one DS master tech guy said it was ok to have these cables connected to the main, ready to plug the charger into, one said it wasnt and DS UK Technical also said it was not a good idea to leave these cables connect, yet theres no current being drawn through them when they are just left connected and not being used.
I,ve now taken the cables off the main 12v battery, but I think I will connect them to the smaller one and do as Andrew has mentioned above.
Jactac, thanks for the detailed post. The guys at my dealership pretty confidently said that while I can use an external charger to keep the front battery topped up, I cannot use it to charge the rear battery directly. The Manual also only talks about charging the front battery with an external charger. Their suggestion was to simply start the car once a week and let the ICE run for 10 minutes to ensure both batteries are charged up.
I am not confident that the guys at the dealership really know their stuff, especially the guys at the service desk. I can’t believe that these two auxiliary batteries don’t get some charge from the traction battery, because my drives are typically short distances and I have gone 2 weeks or more without the ICE ever coming on. Thus far, I have not had to use any external charger for the aux batteries. The car is already over 5 years old and still has the original batteries. So, chances are that my battery issue is simply age related, and as long as the car is used regularly an external charger should only be needed if the car is not driven for extended periods. That is my take from all the discussions and research.
They have no idea what they’re talking about. The small battery is charged while driving, whether the ICE is running or not. The large battery is charged the same way as the small one, plus an additional charge when charging the traction battery from the wallbox (but not the small one). I charge my small battery with a charger and nothing bad happens.
Yeah its confusing with so many different bits of advice.
I’m a bit surprised that the smaller 12v battery just sits there not receiving any charge what so ever.
What is this smaller battery used for ?
The advise from my dealership and DS Uk was a bit of a mixed bag.
The DS master tech at the dealership said due to the low mileage I do and the short journeys, to charge the smaller one from a charger , every so often, as it only receives a small amount of charge from the main 12v battery, which gets its charge from the alternator and/or the traction battery when thats being charged.
He actually advised me which battery charger to buy, a CTEK MX7.
A few months after this advised the car was back in the workshop for something different but because of the battery issues the car had previously they decided to check the batteries again, both failed, yet I was not seeing any errors, thats when they told me to remove the quick connect cables off the main battery.
Unfortunately the DS Master Tech had finished a week earlier at the dealership so I was left dealing with a different tech.
They changed both batteries again under warranty and said to leave the quick connect cables off.
What is the small battery used for ?
So it does get charge from the traction battery whilst thats being charged, and whilst the car is being driven ?
Where does the charge come from whilst being driven ?
It is drawn from the traction battery if you are driving in electric mode, so the more devices you turn on, the faster it will discharge.
So basically, the smaller battery powers the devises, such as heating, A/C, radio ?
And the traction battery then puts charge back into the smaller battery but this only happens in electric mode ?
Is that pure electric mode ?
What about hybrid mode, is it the same ?
The way I’m reading this is that the smaller battery is having a fair bit of usage ?
The small battery is primarily responsible for powering the electric traction control system (hence the “electric mode unavailable” message if it’s faulty), the keyless entry system, and other small items in the cabin. Both batteries are charged when the engines are running, so it doesn’t matter which is charging them (alternator or traction battery), but this depends on the selected driving mode. If the ICE is not running, charging is definitely from the traction battery, as there’s no other power source.
Simply measure the voltage on a small battery when the “Ready” light is on in electric mode. It will then be 14.6V, and the battery can have a maximum of 12.8V at rest.
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Ok thanks,
I’m definitely going to start charging the smaller one.
We have talked about this before, but I cant recall what you said about connecting the cables to the smaller battery.
with the main battery I would connect the live to the live on the battery and the negative to the earth point on the body of the car, but I dont think connecting to an earth point on the car is possible with the smaller battery.
So do you connect both cables direct to the battery terminals on the smaller battery.
if I recall you had a similar charger to mine that came with quick connect cables ?
I have this Ctek quick connector permanently connected to the small battery.
Both cables direct to the battery , not the negative to an earth point ?