Add the ingredients to a slow cooker and cover with enough filtered water to cover.
Set the slow cooker to "low" and cook for 24 hours. You can do as little as 10, or as long as 36- the longer the better in my book unless you don't want it too dark. 24 hours is the sweet spot for us! Stir the broth occasionally (every few hours or so) to keep from burning.
Strain the broth in a mesh strainer over a large bowl.
Cool the broth, and store refrigerated. Use within 4-5 days, and freeze any that won't be used within that time frame.