In a large skillet, cook sausage and onion over medium-high heat until meat is brown. Drain off fat. Transfer meat mixture to a 3 1/2- or 4-quart slow cooker. Stir in refried beans, the 1 1/2 cups cheese, the salsa, and chile peppers.
Cover and cook on low-heat setting for 3 to 4 hours or on high-heat setting for 1 1/2 to 2 hours.
Stir well before serving. If desired, keep warm in the slow cooker on low-heat setting for up to 2 hours. If desired, sprinkle with additional cheese. Serve dip with tortilla and/or corn chips.