Cut the Kielbasa into bite size pieces. Place in a large ziploc baggie. Add the box of brown sugar. Mix the sugar and Kielbasa inside the baggie. Place in the refrigerator over night. Brown sugar will mix with the fat of the Kielbasa and liquefy. Place meat and liquid in a slow cooker and cook on low for a few hours until ready to serve at a party. Can skim off fat from liquid if there is any.