Place the beer and ketchup in a slow cooker on high setting and allow to simmer..
Meanwhile, in a large bowl, combine the ground beef, garlic powder and onion, mixing well. Form mixture into meatballs about 3/4 inch in diameter. Place meatballs in a 9x13 inch baking dish.
Bake at 400 degrees F (200 degrees C) for 20 minutes.
Transfer meatballs to the slow cooker with the beer and ketchup and simmer for 3 hours; sauce will thicken.
