How did you do that if it was completely dead?
Not being able to power on a Fenix does not always mean it is dead and won't come back. When you cannot power on your Fenix or it will not charge when you plug it into charge, a soft reset with it unplugged and then plugging it into charge will often resolve the issue. Not 100% of the time since the issue could be a battery failure or other hardware issues but more than not the steps are successful.
This Support Center article also walks through the soft reset steps if it won't power on or charge.