In a bowl, whisk together the BBQ sauce, apple cider vinegar, brown sugar, onion powder, and garlic powder. Place the chicken breasts in the bottom of the slow cooker. Pour the sauce over the chicken breasts, covering them fully. Cook the chicken on high for 2-3 hours or on low for 4-6 hours. Shred the chicken directly in the slow cooker or remove to shred and return to the sauce. Give the chicken a good stir to coat it in the sauce.