Brown bacon and onion: Add chopped bacon and onion to a large skillet. Season with salt and pepper. Cook over medium heat, stirring occasionally, until bacon is crispy and onion is soft, 10-15 minutes.
Drain excess grease: Remove skillet from heat and carefully drain off most of the bacon fat. Set aside.
Combine in slow cooker: Add all five types of drained and rinsed beans to a 6-quart or larger slow cooker. Add the bacon and onion mixture.
Add sauce ingredients: Top with tomato paste, Dijon mustard, liquid smoke, maple syrup, and chicken broth. Stir everything together until well combined.
Cook: Cover and cook on high for 4 hours or low for 8 hours.
Finish: Remove lid and stir to combine. The sauce should be thick and glossy. Taste and adjust seasoning with additional salt and pepper if needed. Serve hot.