Normally after turning off the ignition, the retained accessory power will operate the windows/radio for 10-15 minutes or until a door is opened. Yesterday after turning off the ignition, I got a message less than a minute later on the touch screen saying that the system was shutting down to save the battery...and to restart the vehicle to maintain the electrical power. Is this a sign that the battery is failing? I have only had the car 21 months (29,000 km) and I have not had any previous battery issues.