When the truck sits for several days the battery would go dead. Finally the dealer decided it was a bad battery and replaced it. Why do I think this is not the real problem and it will reoccur in 6 to 9 months again?
I have no idea why you think it might happen again in 6 to 9 months . But if it starts after you let it set for several days I would think your problem is solved.
The dealer diagnosed a bad battery, so that is probably what was wrong. If they are wrong, and there is parasitic draw, you will probably have problems again before your warranty expires. If you are still uncomfortable, you can have the dealer do a parasitic draw test. You may have to pay for it.