Toast the chiles in a dry medium saucepan over medium heat, turning occasionally, about 5 minutes. Add 2 cups water and the baking soda. Remove from the heat and let stand 10 minutes. Transfer the chiles and liquid to a blender and puree until smooth. Strain through a fine-mesh sieve into the saucepan, pressing the mixture through with a rubber spatula.
Add the cranberries, sugar, maple syrup and 1/4 teaspoon salt to the pan. Bring to a simmer and cook, stirring occasionally, until the cranberries burst and the sauce thickens, 15 to 20 minutes. Remove from the heat and stir in the raisins. Let cool.
Transfer the cranberry sauce to a bowl and refrigerate at least 3 hours or overnight.