My 3 sat in an lot at the train station all week - Monday AM to Friday PM and had a nice long cold soak. Started up instantly Friday evening despite some pretty cold days (temps below -20C the night before). No worries
Then today I sat in line for the car wash and ran the reserve heat for nearly half hour waiting in line. The battery light went off. I guess I've discovered the limits of my battery's tolerance. So much for not sitting and idling
