I’m led to believe that there’s Vcds coding required after replacing the 12v battery, so not quite a diy job (no Vcds coding kit or knowledge!).

is that true r can I just swap it & drive off?

Have a search of the forum, and the answer will be found there - many times over. 

44 minutes ago, 56Doc said:

is that true?

Yes, it's true the battery/car will need coding, however it isn't only VCDS that can do the job. Others can as well, though I don't know specifically which ones.

2 hours ago, Magnet said:

Have a search of the forum, and the answer will be found there - many times over. 

Did try that but nothing came back.

 

Search on ‘Battery coding’ using Everywhere on the drop-down menu. 
Surprised if that doesn’t do it, but Cliff has already given you the answer. Still worth a read. 

Thankyou. 
I’ll have a look

Sadly that found lots of others with various battery related issues but nothing concrete about coding.

so here’s a slant on the issue.

If I connect a 12v supply to the jump points under the bonnet, would that mean I can change the battery without any coding requirements afterwards?

has that been tried before?

24 minutes ago, 56Doc said:

Sadly that found lots of others with various battery related issues but nothing concrete about coding.

so here’s a slant on the issue.

If I connect a 12v supply to the jump points under the bonnet, would that mean I can change the battery without any coding requirements afterwards?

has that been tried before?

A dying battery sees a higher charge than a new one . If the BMS isn't reset ,the car will still charge the new one at the same rate . Thus shortening it's life. Loads of OBD2 scanners out there than can reset the BMS . Icarsoft, Topdon , autel . To name a few.  

A donor power source until the change over is complete, would be beneficial. 

Edited November 29, 2025Nov 29 by Audisq524

1 hour ago, Audisq524 said:

A dying battery sees a higher charge than a new one . If the BMS isn't reset ,the car will still charge the new one at the same rate . Thus shortening it's life. Loads of OBD2 scanners out there than can reset the BMS . Icarsoft, Topdon , autel . To name a few.  

A donor power source until the change over is complete, would be beneficial. 

Thank you, I was hoping it would at least mean the car would be drivable afterwards. But must admit, I don’t see how the BMS wouldnt recognise that the battery was now charged (because it’s been changed.) but, if that’s how it works, it’s how it works.seems a bit OTT. doesn’t exactly prevent theft for parts if all the bad guys can access all the coding tools anyway. I often wonder why they still do it.

The car is drivable after 12v battery change, however it’s advisable to code it. 

On 11/29/2025 at 7:54 PM, 56Doc said:

 doesn’t exactly prevent theft for parts if all the bad guys can access all the coding tools anyway. I often wonder why they still do it.

It has nothing to with theft prevention, and everything to do with ensuring the battery is charged correctly to avoid damage.

On 11/29/2025 at 3:05 PM, Magnet said:

Have a search of the forum, and the answer will be found there - many times over. 

Did try that but nothing came back.

1 minute ago, cliffcoggin said:

It has nothing to with theft prevention, and everything to do with ensuring the battery is charged correctly to avoid damage.

Batteries charged fine from an alternator for decades before Audi slapped a digital BMS in there. Personally, can’t see the reasoning behind it. Certainly don’t see any need. The current & voltage regulator on the alternator was always a simple & effective means of control, also very easy to replace if it did fail.

Individual unit coding was originally introduced to try to prevent theft of the car for parts but as its now common knowledge, coding isn’t really required as it just makes maintenance & upgrades more complicated. & replacing something from another manufacturer becomes almost impossible, even seats! 

a simple ‘reset’ function for the BMS in the MMI would be more than adequate. Same as any TPMS after tyre or wheel swaps. Coding the BMS is just serious overkill. 
Tbh, it would have been as easy for Audi to program the BMS to recognise when a battery has been replaced and reset itself as it was for them to prevent it resetting after its lost power. 

RE-Coding when you replace, renew or upgrade something, requiring specialist equipment is now really just a money making attempt on the part of the manufacturer. 

coding to prevent theft was a good idea but IMHO, its now about 3 decades beyond its use by date as both the kit & knowledge is readily available to anyone including the light fingered brigade,  if they’re prepared to fork out a chunk of cash & learn how to recode. But Im not, as I’d so rarely use it, it’s just not worth the effort 

23 minutes ago, 56Doc said:

Did try that but nothing came back.

Batteries charged fine from an alternator for decades before Audi slapped a digital BMS in there. Personally, can’t see the reasoning behind it. Certainly don’t see any need. The current & voltage regulator on the alternator was always a simple & effective means of control, also very easy to replace if it did fail.

Individual unit coding was originally introduced to try to prevent theft of the car for parts but as its now common knowledge, coding isn’t really required as it just makes maintenance & upgrades more complicated. & replacing something from another manufacturer becomes almost impossible, even seats! 

a simple ‘reset’ function for the BMS in the MMI would be more than adequate. Same as any TPMS after tyre or wheel swaps. Coding the BMS is just serious overkill. 
Tbh, it would have been as easy for Audi to program the BMS to recognise when a battery has been replaced and reset itself as it was for them to prevent it resetting after its lost power. 

RE-Coding when you replace, renew or upgrade something, requiring specialist equipment is now really just a money making attempt on the part of the manufacturer. 

coding to prevent theft was a good idea but IMHO, its now about 3 decades beyond its use by date as both the kit & knowledge is readily available to anyone including the light fingered brigade,  if they’re prepared to fork out a chunk of cash & learn how to recode. But Im not, as I’d so rarely use it, it’s just not worth the effort 

My wife's ford Kuga could be reset using the buttons on the dash  65 reg .  Just buy a used OBD2 scanner or a cheap new one , to do it.  It's always there for EML fault codes etc. the autel 200 is only 40 quid . 

3 hours ago, 56Doc said:

Coding the BMS is just serious overkill. 

As you wish Dave. I'll not waste any more of my time trying to convince you otherwise.

No problem Dave, 

You asked whether the new battery needs coding, and you have been given the answer. Now you seem to want to question that advice and conclude that you ( in caps) have answered your own question, with an answer totally opposite to what you sought an answer to in the first place. 

Good luck when your alternator attempts to overcharge  the new battery, kissing goodbye to any warranty you would have been given. You can then ponder over whether the alternator decides it had enough and gives problems.

For anybody prepared to accept that car technology has changed over the last three decades, here is an explanation of battery coding:

https://www.youtube.com/watch?v=TFK0JPs6aO0

 

I’m not questioning the advice or the fact that the BMS does need coding.

what I’m questioning is the design philosophy behind it as I don’t understand why they changed a perfectly viable system.

 

Why not buy a classic car where you can stick a key in a lock and open and close the doors without any remote, only have 2 warning lights to worry about, no MMI, and above all, if it breaks down you don’t need to plug it into anything? 
‘Design philosophy’ !? I bet you wouldn’t do without your modern toys. 
 

Forgot:- if you want audio,  hold the end of the aerial cable and sing! 

30 minutes ago, 56Doc said:

I’m not questioning the advice or the fact that the BMS does need coding.

what I’m questioning is the design philosophy behind it as I don’t understand why they changed a perfectly viable system.

 

It's called charge cycling .  The system tries it's best to always keep the electronics in tip top shape .  You've got all the safety features ,like Audi sense , the srs system , abs, esp . The list goes on and on.  My car is also mhev , so it's alot of electrics I dare say even Audi techs need help with .  If you just swap a battery over and don't inform the cars brain , it'll be a massive shock to all the systems .  Welcome to the new world.  Say goodbye to points and condensers.  Embrace technology. 😁😄😁

We used to swap the points etc out for an optical system (Luminition) on RN land rovers back in the late 70’s/early 80’s, when we borrowed them for canoeing trips to the Pyrenees & Alps, it improved mpg from 9 to 15! Handy as the fuel wasn’t free!

im not exactly a Luddite though and I’ve had to wrestle and argue from both sides of the ‘why change this, it’s always worked’ and ‘just because it’s always been done that way doesn’t mean it’s still the best way to do it’ arguament when we were redesigning systems for the MoD. Sometimes it’s a no brainer to just go for new, cheap, off the shelf tech or a massive, expensive redesign because the current system isn’t fit for purpose & other times, the effort & cost of redesigning a bespoke system would just be far too disproportionate to any benefit gained to justify.

 

There is a train of discussion that questions whether the current & emerging tech levels are going beyond useful, my Leaf bings & bongs far too much for comfort and it’s virtually impossible to catch the message/ warning indication that only ever comes up for around a microsecond , so rarely actually useful & the lane keeping system, which is ‘always on’ has, on numerous occasions, tried to pull me towards oncoming traffic on the country lanes around me. At least the Audi switches that off below 40mph.

 

the auto braking (again in the Leaf), in the 14 months I’ve had it, has activated when there’s nothing in front of me at least 6 times. It’s quite scary!  Luckily no-ones ran into me when it does it! 
 

technology is generally good but it has to work when needed on’y & not randomly when it gets confused! 
 

 we’ve always had MMI systems, but they used to be just switches!🤣

25 minutes ago, 56Doc said:

There is a train of discussion that questions whether the current & emerging tech levels are going beyond useful, my Leaf bings & bongs far too much for comfort and it’s virtually impossible to catch the message/ warning indication that only ever comes up for around a microsecond , so rarely actually useful & the lane keeping system, which is ‘always on’ has, on numerous occasions, tried to pull me towards oncoming traffic on the country lanes around me. At least the Audi switches that off below 40mph.

 

the auto braking (again in the Leaf), in the 14 months I’ve had it, has activated when there’s nothing in front of me at least 6 times. It’s quite scary!  Luckily no-ones ran into me when it does it! 
 

technology is generally good but it has to work when needed on’y & not randomly when it gets confused! 
 

 we’ve always had MMI systems, but they used to be just switches!🤣

 

Lane assist is the first thing I turn off on every trip.   End of the indicator stalk there's a button to press . I hate it . Alot !! 

Blinking heck! I join Cliff’s stance, so also out on this, except to ask:- so are you going to get the new battery coded or not? 
Or come to think about it, forget the question, since the answer doesn’t really interest me.

Yes, never stated or implied that I wasn’t going to or that it wasn’t needed. 
However, wasn’t quite prepared for it to weigh 22kgs when I picked it up!

This thread appears to have gone somewhat off topic and ended with a ‘political answer’, and it is anticipated that there will be little extra gathered from protracting discussion. 
It is therefore going to be locked.