18v and 20v batteries are interchangeable. But I probably wouldn't use a 24v Kobalt battery in an 18v tool. Kobalt batteries are really closer to 22 or 23v but

18v and 20v batteries are interchangeable. But I probably wouldn't use a 24v Kobalt battery in an 18v tool. Kobalt batteries are really closer to 22 or 23v but still the difference from 18v might be enough to overheat the motor in your tool.