Just a heads up.  Went through the process of replacing the battery in my 2009 base coupe.  I can verify that a group 90 battery does NOT fit.  This is the battery that the GM dealer says is listed for my car.  Interestingly it is also indicated as the size by the online listing from Costco.ca.

The correct size is a group 85 and I had to return the 90 to the dealer who was able to get the 85 to exchange.