Add the frozen meatballs to the slow cooker.
Add the diced white onion and barbecue sauce. Stir.
Cover and cook on high for 2.5 hours or on low for 4 hours. Stir occasionally so the meatballs won't burn on the edges.
Serve as an appetizer with toothpicks or as dinner on top of mashed potatoes or rice. Or you can serve on slider or hoagie rolls.
After the cooking time is up, set the slow cooker to the warm setting.
The meatballs can be kept warm for up to 3 hours. Check on the meatballs occasionally and stir. Add a splash of water if sauce seems to be dry.
