had that happen too me today...took the battery to autozone and they recharged it and tested...tested good...this time

 

My 05 GT is at the dealer right now for this issue. I store mine as well over the winter but I usually start it up every week or 2 and this was the first time it was dead. I also read, I think it was in a TSB but don't remember, that if the battery is cold it won't take a charge for the first 4 hours. I should get the car back today or Monday. Will let you know what the dealer says if I can find this post again.

 

Here's a TSB for a discharged battery:

http://www.stangnet.com/images/stori...Bs/05-9-18.pdf