Yes there is downside as a lot of electronics need to be reset. Also the automatic window lowering on door opening/closing won't work so you can't open and close the car doors without potential damage to weatherstripping. I think a float charger such as C-Tek is a wise investment and very convenient and pays for itself by extending battery life.I'm planning to store my newly arrived 2013 SLK55 AMG for the winter. It will be 5 months while I'm in Arizona. The car will be covered in a heated underground garage at my condo. Are there any down sides to battery disconnection?