My 2004 Cadillac cts v-6 battery was dead had not started it for 2months so i go

Good Morning You may have a charging system that is not working properly or something is staying on in the car draining the battery. The charging system will need to be tested and it is working properly then the electrical system will need to be tested for a voltage drain. It could be as simple as a light staying on in the trunk or glove box. I hope this helps if you need more help please give us a call to schedule an appointment at 410-944-6850 Thanks for your time Bobby