As you rightly said i believe that my car has been stuck in power saving mode, and hadn't learnt about the new battery.
This is how i fixed it for any poor souls who are still trying;
1. Viewed the state of the battery in VCDS under 19-CAN gateway > Measuring Blocks > Groups 18,19 and 20
2. Noticed that the battery state of charge was healthy at 77%, but the battery state in MMI was at 10%. This value did not change which explains why the low battery warning was always displayed. After monitoring for 15 minutes with the ignition on, the state of charge was increasing, but the MMI display information did not alter.
3. I viewed the current BEM code in VCDS under 19-CAN Gateway _> Long Adaptation -> Channel 4 -> Battery identification). The code that was stored here was different to the BEM on the battery, so i knew that it hadn't been applied.
4. I applied the BEM code in the following manner - Part number i kept the same as before, then entered the new information as follows;
- (N) Part number - (11 digits) - kept this the same as the previous battery.
- (V) Vendor code - (3 digits) - in my case VA0 for Varta
- (S) Serial number (10 digits, but leaving out the starting 3 digits of manufacturer)
NNNNNNNNNNN VVV SSSSSSSSSS
5. Restarted the car, and behold, the MMI battery state was at 100%!
Battery is charging fine, and the car is now out of power saving mode and running perfectly!
I think the rule of thumb here is that if the battery is replaced before the car goes into power saving mode, then it will probably learn about the new battery itself. If the 10% MMI state has been reached, then it will need coding.
Important to note that this battery was an Audi OEM, hence the BEM code being visible on it - so anybody who is thinking of doing a battery change themselves, i would suggest spending a bit more and using an OEM to be sure.
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