Anyone fitted a new battery in a A4-B8 late 2008 ? - conflicting info

[headache56]

What battery should I use ?

- EKTA shows 9 different capacities of battery ranging from 61Ah to 110Ah. I live in London so I do not think I a need Siberian-weather capable battery.
- My existing battery is a Varta 61Ah battery 242x179x190 (LxDxH in mm)
- UK internet Battery sellers variously quote lengths as 242mm or 278mm. I am not convinced all understand the 10-digit BEM code process.
- I am thinking of using a Varta E11 (77Ah and 278mm length) but I do not know if that
has a 10-digit BEM / battery code that the B8 expects to be coded via my VCDS. I think (hope?) that both 278mm and 242mm batteries can be held securely.


Whether to use a Back Up power supply when replacing battery

- ELSAWIN says yes, Connect a battery charger to provide backup power supply (

Electrical system; General information; Rep. Gr.27).

- I cannot get my hands on the owner's manual (my wife has the car for a few days) but IIRC it suggests that one does not use a back-up power supply.
- Some posters on lesser web sites suggest using a back up power supply to preserve settings.
- Other posters suggest it is bad or unnecessary to use a back up power supply e.g. in case there is an increased risk of setting off an airbag. They also say they have not lost any settings.
- I am thinking, as I have VCDS I can probably reset any codes so why take any risk - therefore I don't propose to use a back- up power supply.

Any UK user actually replaced a battery on a A4 B8 please ?

[headache56]

Ah update:

- Found the driver's manual/quick start quide and no mention found on whether to use a back up power supply.

- Spoke to 4 battery suppliers and none could confirm if a new battery comes with the necessary 10-digit BEM code, in fact 3 didn't understand the question (apparently).

- Will probabaly use a back up power supply after all, be careful that no terminals etc touch body, and replace the battery with the exact same brand, size and capacity type so even if no code is available the worst that will happen (I hope) will be that the Power Managment Controller will assume it is the same battery as before.

- Searching on an unverified source on Google suggests that a typical battery giving say 100% power at 25c+, gives about 65% of that at Oc and 50% at -18c.

[John140]

I have seen a number of posts about batteries on B8 A4's being dead etc, this is a bit worrying really, why are batteries little over 3 years old failing like this ? On the subject of the larger capacity batteries, the very high AH batts may be for cars fitted with the start-stop feature. My car has this and the battery (in the spare wheel well) looks physically larger than my last diesel A4 had.

[headache56]

Useful info:

http://bannerbatterien.com/banner/fi...echnik_GB3.pdf

[sportq]

So, this morning the low battery message came up on the centre display. I knew the battery was weak, I'd enabled the battery meter with VCDS and it was struggling to get above 70% on a long run and during the week it was typically around 50%. The cold the morning and 165,000 miles seems to have finally killed it.

Has anyone sucessfully replaced the OEM Audi battery (Moll brand, seems unobtainable in the UK) with a generic one without a BEM code? As mentioned above, I have VCDS so I could code it if needed.

Could I just use the BEM code from another battery? I guess there is some sort of checksum in the code that would prevent anyone just inventing them.

Just spoke to Euro Car Parts both online and my local branch and got two different answers. The online guy said it needs a battery with a BEM code, the local branch says as long as it fits it's good to go!

Peter

[Guest 2]

If the voltage or amps etc isn't gonna change in the new battery then coding is not needed from reading on here.

[Dieseldoos]

If you have stop\start then the reason for coding is because the system moniters the battery and charges when needed, so basically you are telling the car it is a new battery. (Same as it automatically re starts
If the voltage drops to a certain level)
You can swap the battery without coding, and the car will “learn“ the battery and adjust as needed, but not straight away, so basically the coding helps with over charging from the start.

[sportq]

Update, just been into ECP. All their recommended replacements (Bosch,Lion,Exide) are all 72Ah and physically much smaller than the Moll OEM fitted by Audi. The original one is 95Ah so I told them to keep it.

I agree that there's no way the coding should affect the car but the info here: Audi A4 B8 Battery Coding - AudiForums.com backs up what Dieseldoos said, when the coding is changed it triggers the car to re-learn the charge/discharge profile of the new battery and re-enable systems it may have turned off to conserve power.

I've had a good look at the battery under the spare wheel and there's a metal bracket the goes over the top of it which the space saver is then bolted down to. A non-OEM battery might not physically fit or might fit but wouldn't allow the bracket to be re-fitted. Anyway, I've bit the bullet and got a replacement being delivered from Perth Audi this afternoon. It's £50 more than the generic ECP lower capacity ones so not too painfull.

Peter

[headache56]

Hi Peter,

Please see my posts on this subject.

[sportq]

Update....

Fitted the new Audi OEM battery, Varta this time, noted then BEM code, charged up the Netbook I use for VCDS and...... there's no battery management in my B8. No controller at address 61. What gives? Is it only on MMI cars?

The car quickly figured out I have a new battery as it went from 80% to 100% charge in less than 5 miles. The old battery wouldn't get above 70% a regular 80 mile trip to Dundee.

Peter