Place the chicken thighs in the bottom of your slow cooker.
Sprinkle the au jus gravy mix, ranch dressing mix, and chili powder evenly over the chicken.
Add the drained white kidney beans, pepperoncini brine, fire-roasted diced tomatoes, and sliced pepperoncini on top.
Finish by placing the butter slices evenly over the top of the ingredients.
Cover the slow cooker and cook on High for 3–4 hours or on Low for 6–8 hours, until the chicken is fork-tender.
Midway through cooking, stir everything gently to ensure flavors are well distributed.
Once cooked, remove the chicken thighs and shred or chop into bite-sized pieces.
Return the chicken to the slow cooker, stir to combine, and taste for seasoning. Adjust salt or spice as needed.
Switch the slow cooker to the Warm setting and serve hot.