Heat (or cook) the meatballs as directed by the packaging or recipe.
When cooked, place the meatballs in a slow cooker.
In a medium bowl, mix the grape jelly and chili sauce, then pour in over top of the meatballs. Stir to completely coat.
Cook the meatballs on high for 1 to 2 hours, Stir the meatballs, then reduce the heat to low until it's serving time.
During serving, keep the meatballs in the slow cooker on the warm setting and stir occassionally (to keep the sauce from thickening).