Heat a large pot or saucepan over medium heat. Add the bacon and cook until it's just turning crispy, 3 to 5 minutes. Add the onion and garlic and sauté until translucent, another 3 minutes. Stir in the beans, beer, ketchup, chili powder, brown sugar, and cayenne. Simmer until the sauce thickens and clings to the beans, about 15 minutes.