Members - my 2018 A6 Allroad on occasion when I start it tells me the STOP/START SYSTEM UNAVAILABLE - SYSTEM FAULT or an ESP fault. This is not every time, but on occasion. Does this require a visit to the dealers ? The car is under warranty so it’s not going to cost, but I’m wondering if it’s a symptom of another issue like the battery beginning to fail.

Any thoughts from yourselves ?

Hello Ian,

Cutting to the chase, I would suspect a failing battery - below acceptable parameters in some respect. 
You may find that the fault gets ‘blamed’ on the amount the car is driven ( if it doesn’t get a sensibly long run a couple of times a week).

Beware of being recommended to keep the battery charged - you will need an up to date ‘intelligent’ charger- since this may extent the issue outside the warranty period. 
Typically, the stop/start is the first thing that gets affected when the battery gets below par, even though you will find that the car starts without issue, even on cold mornings. Batteries just don’t last as long as they did - understandably? 
I would be persistent in sorting this out under warranty, and would most certainly be keeping a record of all dates and actions.

Kind regards,

Gareth. 

Thanks very much. I’m on it now !