Happened to my Audi A3 yesterday. Came with the dreaded run the battery whilst stationary. drove for 5 minutes then said to me to come to safe stop with red warning. Managed to get it down to mates garage who told me it was a alternator issue as battery wasn't charging. As soon as he tested and switched car on the full car collapsed and everything switched off. On the phone for Blackburn Audi the part alone is £1600 and labour for a 8 hour job is £1500. Said we could run diagnostic and get you some goodwill from AUDI UK but not guaranteed. Reading up on these forums it seems its a common issue on the MHEV. Need to get it recovered to AUDI garage now but wont be able to run a diagnostic for 1.5 weeks. What a joke of a company.