Pour the beans, crushed tomatoes and diced tomatoes into a slow cooker and turn to High heat.
Brown the ground beef in a large skillet over high heat until it is crumbly and no longer pink. Drain off any grease and stir in the chili seasoning packet. Cook one minute then stir the beef into the tomato mixture.
Cook the onion in the same skillet over medium heat until they have caramelized, about 15 minutes. Stir into the slow cooker along with the cayenne pepper. Add a little of the cayenne pepper at a time. It takes a little while for the heat from the cayenne to come out in the chili so taste often.
Cover and cook on High for 2 to 3 hours until the beef is tender. Stir occasionally as the chili cooks.