Hello Paul,
As I’ve said before, and I think as Steve has confirmed- Halfords battery testing may not be totally adequate in terms of assessing all of the parameters which assesses the total efficiency of the battery. I have certainly confirmed that with a just-out-of-warranty non-Audi.
You could find that genuine VAG diagnostics may pick up some issue with the battery in some respect - say for example cold cranking current below par.
I appreciate VAG diagnostics can be expensive, (independent?) but I would be asking, are you prepared to pay to replace any number of components before firmly establishing that these issues aren’t battery associated?
Kind regards,
Gareth.