Mine failed just short of 2 years, 14k miles. Covered under warranty (explicitly "warranty" rather than "goodwill" - they have those categories on the invoice, the battery was "warranty" while checking the tyre pressures and the wash they would have done if I wasn't in a hurry were "goodwill".)
Factors making my usage worse than average in terms of stress on the 12V battery:
Edit - to be clear, mine didn't actually "fail" - the warning message came on saying it needed replacement, apparently triggered by the charge/discharge interval becoming shorter, implying the 12V battery has lost capacity. Not clear how much longer I could have gone on before it actually did fail (waited about 5 days from message to repair in this case).
Factors making my usage worse than average in terms of stress on the 12V battery:
- I don't commute and most of our local transport is by bicycle, so low overall mileage and the miles I do compressed into few days - quite a few days when the car sits doing nothing, draining away on the 12V.
- The car is parked right outside the front door, and my wife carries the keyfob in her handbag. So every time she leaves the house on foot/bicycle, the car wakes up and extends its handles etc - using 12V power.
- There was some sort of bug in 6.x software causing the car to remain awake, silently playing music (I could tell from watching WiFi activity), again wasting 12V power.
Edit - to be clear, mine didn't actually "fail" - the warning message came on saying it needed replacement, apparently triggered by the charge/discharge interval becoming shorter, implying the 12V battery has lost capacity. Not clear how much longer I could have gone on before it actually did fail (waited about 5 days from message to repair in this case).
