Gather all ingredients.

Place soaked and drained navy beans in a large saucepan with 4 cups of water per 1x recipe. Bring to a boil over high heat, then reduce to medium-low, cover, and simmer for 1 hour.

Preheat the oven to 375°F (190°C).

In a small bowl, mix ketchup, maple syrup, brown sugar, molasses, Worcestershire sauce, salt, black pepper, and chili powder. Set aside.

After simmering, drain the beans, reserving the cooking liquid.

Transfer the beans to a 1 1/2-quart casserole dish (adjust for larger batches). Stir in the chopped onion and prepared sauce mixture.

Add enough reserved cooking liquid to cover the beans by about 1/4 inch.

Cover the dish and bake in the preheated oven for 10 minutes. Reduce heat to 200°F (95°C) and bake for 6 hours, stirring halfway through.

Once beans are tender and the sauce is thick and sticky, remove from the oven, stir, and let stand covered for 15 minutes before serving.