Preheat the oven to 400 degrees F (200 degrees C).

Place chicken bones, carrots, celery, onion, and garlic cloves on a baking sheet; drizzle with olive oil. Toss to coat.

Roast in the preheated oven for 30 minutes, stirring halfway through.

Transfer roasted bones and vegetables to a 6-quart slow cooker. Add vinegar, bay leaves, salt, and peppercorns; cover completely with water.

Cook on Low for 24 to 48 hours (but not any longer), adding 1 to 2 cups more water during the cooking process as needed to keep bones submerged. Strain broth using a fine-mesh strainer. Pour into jars and refrigerate until ready to use.