Prick each potato all over with a fork and rub with 1/2 teaspoon of olive oil and a sprinkle with salt. Wrap each potato in a square of aluminum foil.
Arrange the potatoes in the slow cooker so that they fit snugly next to each other. If you are baking 1 to 2 potatoes, set them in the middle of the slow cooker; for 5 or more potatoes, stack them in 2 layers.
Cover the slow cooker and bake for 8 to 10 hours on low. The potatoes will be ready after 8 hours, but can be cooked for up to 10 hours. Do not leave them on the WARM setting for more than an hour due to food safety risks.
For crispy outer skins, preheat oven to 350 degrees F. Remove potatoes from foil and transfer to a baking sheet. Place potatoes in the center rack of the oven and bake for 10 minutes, until potato skins are crisp.
To eat, remove potatoes from oven, split in half and top with toppings as desired.