All sausages fall into one of two categories: fresh sausage, such as fresh kielbasa or bratwurst, and pre-cooked sausage like smoked sausage or knockwurst, according to the National Hot Dog & Sausage Council. Both can be prepared in a slow cooker, though you'll need to follow a different method depending on the type. Pre-cooked sausage needs to be heated through, while fresh sausage, which is raw, needs to be cooked for a longer amount of time to ensure it is safe to eat. All types of sausage are high in sodium, fat and saturated fat; eat sausage in moderation and only occasionally, especially if you have high blood pressure or heart disease.
Place pre-cooked sausage links in the bottom of the slow cooker. Put the lid securely in place.
Turn the slow cooker to the high setting and allow the sausages to cook for two hours, or set the cooker to the low setting and cook the sausages for approximately four hours.
Use tongs to remove the sausages. Serve immediately, or turn the slow cooker to the warm setting, if available, to keep the sausages warm for several hours.
Heat olive oil in a large skillet and add whole or sliced fresh sausage links. Use a fork to prick each whole sausage in several places. Brown the sausages on all sides.
Transfer the browned sausages into the slow cooker. Add vegetables like sliced bell peppers, sliced onions, cubed potatoes, carrots or cabbage wedges, if desired. Pour in liquid such as water, broth, red wine or tomato sauce, planning on one-third cup of liquid for every 2 pounds of fresh sausage.
Allow the sausage mixture to cook on low for six to eight hours, or until a meat thermometer registers 165 degrees F and there is no visible pink in the center of the sausage.