Place brats and onions into a pot. Pour beer over the brats and onion.
Turn meat to medium-high. Bring to a light simmer and cook for 15 minutes.
Heat grill to medium-high heat. Remove brats from beer and reduce heat to medium to allow onions to continue to cook. Place on grill and cook 3-4 minutes then flip to cook the other side.
Remove brats from grill and serve with onion and desire toppings. If they need to be kept warm for a period of time place them into the beer and onion pot to keep warm until ready to serve.