There is not much in there that a little snow could hurt. Some owners spray their engines just to keep them clean. My guess is that your might have a bad connection at the battery or perhaps at the new alternater. I would check that first, then if you have a multimeter, connect it to the battery post. It should read approx 12.6 volts with nothing on and then get a someone to start the engine. You should see the reading go up to about 14 volts with the engine running about 1500 rpm of above.
Also, which model of Optima battery did you install and did you have to lay it sideways? When in went on their site all the batterys were about 1/2 inch too tall for the Cobalt.
Last edited by Oldkid; 02-08-2011 at 07:44 AM.