In a small skillet, cook the bacon over medium-high heat, stirring, until browned, about 5 minutes. Transfer to paper towels to drain. Drain off all but 2 tablespoons of the drippings, add the onion to the skillet and cook, stirring often, until soft, 5 minutes. Stir in the ketchup, brown sugar, vinegar, mustard and chili powder to combine.
Place all the beans and the chickpeas in the slow cooker and add the onion mixture and bacon; stir to combine. Cover and cook on low heat until thick, 6 hours.
