Preheat the oven to 350 degrees F.
Line a plate with a paper towel. In a saute pan over medium heat, add the bacon. Cook until tender and cooked but not crisp, flipping once, about 8 minutes. Remove to the paper-towel lined plate. Let cool and then chop.
To the pan with the bacon drippings, add the onion and cook until tender, soft and translucent, about 7 minutes. Add the garlic and cook until fragrant, another 1 to 2 minutes. Remove from heat.
To a large bowl, add the baked beans, molasses, dark brown sugar, barbecue sauce and bacon mixture. Pour the mixture into a 9-by-13-inch baking dish and bake, uncovered, for about 1 hour. Remove from the oven and let cool for at least 10 minutes before serving.