Preheat the Indoor/Outdoor grill on Setting 4.
In a large saucepan, bring the brats, onions and beer to a boil. Turn the heat down to medium and continue cooking for 12 minutes.
Drain the beer from the brats and onions, and return the onions to the saucepan. Place brats onto the preheated grill and put the lid on. Grill for 10 minutes per side.
Meanwhile, melt the butter with the onions, sugar and salt on medium-high heat. Once the butter is melted, turn the heat down to medium-low and allow the onions to caramelize, stirring occasionally.
Top the brats with the caramelized onions.