Importance of 12v battery registration?

[oldgitdave]

Hi all, so you may have read my thread Car Dead. Anyway, since then I've had a couple of 12v battery low warnings and I've been using a Ctek battery conditioner to keep it topped up but thinking it's knackered tbh as @karbonfaiba suggested.
Yesterday I took the car off the Ctek to take my (85 yo) mother to the doctors and had to wait about 45 minutes for her to return. Car all switched off but I listened to the radio and decided to sort my favourite stations. So mum returns and I press the start button....loads of bings & bongs, 12v system failure, electric drive system failure, contact your garage etc.
After plenty of swearing I got it going using my 800A car booster connected to the under bonnet connections but the 12v warning light was on all the way home (2 miles or so, that's all). Decided to buy a new battery via Tanya batteries. EFB, the same as original, 60A compared with 59A original. Different make but otherwise the same.
I used the Erwin information to make the change but it does say.. "Adapting battery monitor control unit J367After installing a new starter battery or a new battery monitor control unit -J367-, battery monitor control unit -J367- must be adapted."

I fitted it this afternoon and the car started fine. A few error messages popped up but soon cleared, all seems good I'm glad to say. Just wondering whether I need to get it coded to the new battery? Any issues if I don't?

 

[CupForm]

I'm not sure how it works in the case of VAG PHEVs, but as much as I've read on various battery topics of different car brands, I would say that the 12V charging management:
- should know the exact parameters of the new battery (if it's not identical to the previous one);
- should get a reset even if the battery is identical. The old one was unavoidable loosing some of the original capacity, and the 12 V charging management was acting accordingly. A reset is needed such that it would "forget" the old/sick battery and start "learning" the new/healthy one.

On top of that, I think that in the case of PHEVs the 12V charging management is a bit more complex than the ICE one, so it needs a bit of extra care - I would definitely check with the dealership if I were you.
BTW, was the original battery no longer covered by warranty?

 

[Karbonfaiba]

As suggested, you should reset the battery management system manually after the battery change, so this J367 control unit is probably that - it detected anomalous readings and throws a DTC.

I don't think anybody has leaked the hidden sequence on MQB-Evo cars yet, so you will unfortunately need a device like OBDEleven, VCDS, Carista, etc. to send the reset command. Maybe it doesn't exist for WV, but engineers always build shortcuts, a combination of pumping the brakes and flashing the lights is what Ford had at least.

If you replaced with the same type of battery, i.e. EFB - it won't need programming and a BMS reset will relearn the capacity. Not doing it - isn't dangerous or anything - but I'll be surprised if start/stop system works. MQB platform is apparently really sensitive to slightest changes, any errors can be ignored on the first restart.

Re: battery registration - it's an uphill battle to get any 12V battery replaced under warranty as it's considered a normal wear and tear part, but it will have a warranty which is registered by the dealership or garage who installed it, or direct with the battery manufacturer (if self serviced). TBH I think you saved yourself a lengthy headache and made the right decision, way too many advanced systems rely on not just a working 12V battery but a healthy one too.

 

[oldgitdave]

Thanks for that. I'll see if my local garage can do the required coding. It looks fairly simple from what I've read but I don't have the kit to do it.

Waste of time going to the dealer with this as it's a minimum of 4 weeks wait to get anything done there.