Combine the chicken thighs, vinegar, soy sauce, garlic, peppercorns and bay leaves in a large pot. Cover and marinate the chicken in the refrigerator for 1 to 3 hours.
Cook the chicken on Low in the slow cooker , cover for 5 hours, stirring occasionally. Remove the lid and simmer until the sauce is reduced and thickened, about 20 more minutes. Serve with steamed rice.