Using a slow cooker is currently my favorite way to make chicken stock. One of the challenges with making stock or chicken broth (technically, I think the “broth” recipe linked here is actually still stock since it uses bones) is keeping the liquid at the brink of a very slow boil (I aim for keeping the liquid between 190° – 200°F / 88° – 94°C) over the entire cooking time so that the stock does not become cloudy. The slow cooker method never brings the liquid to a boil avoiding that concern.
Additional flavorings such as onions, heads of garlic, leeks, celery, radishes–really anything you’d like–can also be added. I used to save various scraps such as ends of onions, celery tops and leaves, etc. in the freezer for use in making stock later. However, these days I tend to make a pretty basic stock and add other flavors when using it for cooking. Finally, while I have not really noticed a difference, cutting some larger bones in half also exposes the marrow inside it, which some things I’ve seen on the Internet say adds more flavor.
While I have a pressure cooker that is able to reach the “high” pressure needed for food safety when canning chicken stock, that is something you should only do at your own risk. Therefore, I will not talk too much about the process other than at my elevation using quart containers, I “can” the stock for 25 minutes at 15lbs of pressure with a natural release at the end. For shorter-term (and arguably safer) storage, the stock freezes well as long as you leave space in whatever container you use as the stock will expand when frozen. Making ice cubes out of the stock is also a good way to have pretty much any amount of stock on hand without having to worry about having stock left over that needs to be used within a few days for something else.
A full written recipe may be found here: https://cook.karylstein.com/g/family/r/slow-cooker-chicken-stock