Heat beer, onion, ketchup, barbecue sauce and mustard in a slow cooker.

Preheat grill to medium-high heat (325). Place bratwurst on a grill. Cook on one side for 3-5 minutes-and turn over-(being careful not to poke or burn brat). Allow cooking for another 3-5 minutes or until juice begins to seep from the brat. Remove immediately! Brats will not be fully cooked-just seared on the outside.

Place brats into the crock pot and add water until brats are completely covered. Simmer for 1-2 hours on high, or 4-6 hours on low. Serve in bratwurst buns, with sauerkraut, ketchup, mustard, and onions.