In a large bowl combine kidney beans, black beans, onion, celery, peas, sweet pepper, soup, garlic, thyme, and pepper.
Spoon half of the bean mixture into a 3 1/2- to 4-quart crockery cooker. Top with the potatoes and remaining bean mixture.
Cover and cook on low-heat setting for 8 to 10 hours or on high-heat setting for 4 to 5 hours. If desired, top individual servings with cheddar cheese.