Combine beans, tomatoes, garlic, sage, and 3/4 cup oil in a medium pot. Add cold water to cover by 1″ (about 2 1/2 cups). Bring to a boil; reduce heat to medium-low and simmer, partially covered and adding water by 1/4-cupfuls as needed to keep beans submerged, until tender, 35–45 minutes for fresh or frozen and up to 1 1/2 hours for dried.