AGM battery replacement without VCDS... issues?

[YTee]

So, hypothetical situation...

Replacing the battery in a 2010 A3 (8P) with Start/Stop. Say I replace the battery... like-for-like AGM battery... same size/capacity/type... but I don't do a reset via VCDS because I don't have access to VCDS... dun dun dah!

What issues am I going to see? Obviously the car will start and run... that's a given. But what else? Will I get an over-charged battery and therefore a shortened battery lifespan, or perhaps an undercharged battery eventually causing starting issues. Will I get key fob/immobiliser issues? Will it turn purple?

All authoritative answers or educated predictions received with thanks. I know what Audi *say* to do, that's not what I'm interested in. I'm interested in actual facts... pure truth... science

[Adrian E]

It won't learn the new battery specs, so will assume it's the old battery continuing to age. That, from memory, means it'll change the charge profile and potentially interfere with stop-start function eventually. You are right that the world won't stop spinning, but it's worth getting it done if you can.

Coding it with VCDS takes a couple of minutes - local indy can do it, or just find someone that lives locally to you that has it. I've done a few for people over the years.

[stevemcs]

Is it AGM ? most of the Golf segment cars run EFB battery's and they don't normally need coding.

[320d is all you need]

Many garages will be able to code it for £20 - or find someone who has the VCDS or Carly type app on a friendly owners page

[catso]

Does it need to be coded?

Asking because my Son has a 2011 Golf on which we replaced the battery and it doesn't have the coding option so not required, would think A3 is probably the same?

[stevemcs]

I've never seen one that needs coding, they are not normally AGM batteries either. Life seems to be 24-48 months on VW's before they start to fail.

[320d is all you need]

catso said:

Does it need to be coded?

Asking because my Son has a 2011 Golf on which we replaced the battery and it doesn't have the coding option so not required, would think A3 is probably the same?

can very from model to year.

Worth checking.

[YTee]

Thanks everyone. Sorry for the delay in reading the replies.

It is an AGM yes, I checked the manual and the existing battery. Its because it has start-stop (sigh).

I do have Carly for VAG, but it doesn't support battery reg. Carly for BMW does it seems, but not VAG.

I'll come clean, I've done the battery change (like you hadn't guessed). So far, no problems at all.

Obviously I could just get vcds, or throw it into a garage for a reset, but I'm just really really curious about whether that is genuinely necessary on a 'relatively' simple car like the 8P. Can't seem to find anything truly authoritative about that.

[stevemcs]

You can have an EFB battery with stop start, have you scanned the car for faults ? Run diagnostics and clear all fault codes, as an example Minis need to be coded, but it will take 6 hours before it will even start to consider stop start, however they also suffer from a sensor that sits in the brake servo, these fail and also stop the stop start from working.