Add the brats and onions to the bottom of a deep skillet. Add enough beer to cover the brats. Bring to a boil. Reduce heat and simmer until the brats are cooked through, the internal temperature has reached 160 degrees F.
Remove the brats from the pan and set aside the beer and onion mixture.
Place the brats onto a hot grill and grill until golden brown and return to the beer mixture until ready to serve.