Spray 10 inch skillet with olive oil cooking spray.
Add olive oil and heat skillet to medium heat.
Sauté onion, stirring as needed for 5 minutes.
Add garlic and continue to sauté both onion and garlic for 10 minutes. (The lower heat will prevent burning and allow longer sauté time.)
Spoon onion and garlic into slow cooker.
Pour heated water into slow cooker. (The heated water gives the dish a head start in cooking. If preferred, use cold or hot tap water. Remember, if additional water is needed once beans have started cooking, heated water is necessary to prevent discoloring of beans.)
Add chipotle chile pod.
Cover slow cooker; turn heat to high setting and cook for 8 hours. Add heated water if beans lose too much water. Beans may be ready in as little as 5 hours. Taste test as needed. Longer cooking time adds flavor.
Toward end of cooking cycle, add salt and stir.
If thicker consistency is desired, puree 1 cup of beans and stir into slow cooker.
Remove chipotle chile pod. Discard or use as desired.
Serve with warm tortillas. Refrigerate for up to 3 days or freeze for later use.