My S1 has had the odd ECU error (left bank too lean) come up usually with cheap supermarket fuel or when restarting in the cold & damp. Rarely I also got this for the other bank.
I bought an OBD2 dongle and a "torque" app to turn the warning off as most Roadster owners do.
The car also occasionally was hard to start when hot. I bought spare relays in case of failure.
The car of course was always overnight on a charger.
The 3 weeks away in Italy showed that the error warnings started coming up every day at a hot restart.
The poor starting got worse.
So I set up a day with Krazy Horse for them to look at it next month.
When home & in the garage the 12 year old original banner battery had the good grace to fail rather than on the road.
With a new battery the issues have vanished.
I suspect the ECU is sensitive to a weakening battery and 3 weeks off the charger exacerbated the issue.
So maybe if you get those symptoms it is the battery not the ECU or the starter.
