Add the onion, bell pepper, garlic, all three beans, both tomatoes and broth to a 6-quart slow cooker.
Stir in the chili powder, cumin, paprika, cocoa, chipotle and salt until the spices disappear into the liquid.
Cover and cook on low until the onion and pepper are fully tender and the broth tastes integrated, 5 to 6 hours.
Mash 1 cup of beans against the side of the cooker if the chili needs more body, then stir them back in.
Cook uncovered on high for 10 to 15 minutes until the surface looks thick rather than watery.
Taste for salt and chipotle heat before serving.