In a large bowl or stock pot, add 8 cups of water. Add dry beans and let them soak overnight. Drain the next day, reserving most of the liquid. Set aside.
Preheat oven to 350 and add ketchup, maple syrup, brown sugar, molasses, Worcestershire sauce, onion, salt, pepper and chili powder to a 9x13 baking pan with high sides and whisk well. Add beans and mix to evenly coat. Spread beans in an even layer.
Add reserved bean water and if necessary, or additional water, so water covers beans by 1/4 inch. Cover tightly with foil.
Bake for 40 minutes. Leaving beans in oven, reduce temperature to 200 degrees F and cook for another 3 hours. Remove foil and stir beans.
Return foil to the top and cook for an additional 3 hours or until beans are tender to your liking, and sauce is slightly reduced. Remove from oven, stir. Let stand 15 minutes before serving to continue thickening.