Just following up with my own experience after three days of towing my C-Max. I've been leaving it in Acc mode (from the Off mode, pressing the start button once without holding down the brake pedal). I checked on it at each gas stop and at the end of each day. At least three of those times it appeared to be off when I got in the car, so it must time out after a period of time. On two other occasions, the Sync/Nav display flashed a message that said it went into power save mode to conserve the battery, and one of those times I had trouble waking it up. Pressing different combinations of the start button and brake pedal wouldn't wake it. I got out of the car to tell my wife to turn the key on the motorhome, and when I got back to the car it started right up, so either the charge line power woke it up, or just me getting in the car again reactivated something to get it out of "sleep" mode.
