Place meatballs into the bottom of the slow cooker. You don't need to thaw them; they will cook perfectly from frozen.

In a separate bowl, combine the chili sauce and grape jelly.

Stir the mixture until the jelly and chili sauce are well blended.

Pour the grape jelly sauce over top of the meatballs in the slow cooker, ensuring that all the meatballs are coated evenly. 

Cover with the lid and let the meatballs simmer in the sauce for on low for 4-5 hours or high for 2-3 hours, stirring occasionally.

Once the meatballs are hot, cooked through, and the sauce has thickened, they are ready to serve.

You can keep the slow cooker on the "warm" setting if serving them over an extended period.

Store leftover meatballs in an airtight container.