Where is the missing power consumption coming from?

My laptop (Dell Precision 7550) has been running extremely hot and consuming battery very quickly, even with no applications running. According to powertop, when running nothing but gnome and a single terminal, the system has been drawing in the range of 40-50 watts. However, according to the same tool, the power consumption for individual hardware components, such as CPU, GPU, RAM, display, radios, etc. only totals to around 4 watts. How can I diagnose what's consuming the missing 40+ watts? I have disabled the discrete graphics card. Every process monitoring or cpu monitoring tool I have tried is reporting the cpu load is as close to zero as one could reasonably expect.