Prepare the Ingredients:
Slice the kielbasa into bite-sized pieces. Peel, core, and dice the apples into small chunks.
Make the Sauce:
In a mixing bowl, combine the barbecue sauce, brown sugar, and apple cider vinegar (if using). Stir in the cinnamon for added warmth.
Add Ingredients to Slow Cooker:
Place the kielbasa and diced apples into the slow cooker. Pour the sauce over the top, and stir to coat everything evenly.
Cook on Low:
Cover and cook on LOW for 3-4 hours or HIGH for 1.5-2 hours, stirring once or twice to ensure even cooking.