Place the frozen meatballs in the bottom of a 6-quart slow cooker.
Sprinkle the ranch seasoning mix and au jus gravy mix evenly over the meatballs.
Scatter the pepperoncini peppers on top and pour in 2 tablespoons of the pepper brine. Place the butter on top of everything.
Cover and cook on LOW for 4 hours or HIGH for 2 hours, until the sauce is bubbly and the meatballs are heated through.
Gently stir to coat all meatballs in the sauce. Serve warm straight from the crockpot with toothpicks.