1) Open Task Manager so you can observe the CPU performance.. right-click the graph and change to "show logical processors" to make sure the right number of threads are there (should be EIGHT).
2) Make sure the CPU usage is already relatively low before starting anything (maybe 5% or so)
3) launch Unigine Heaven so you can record the average FPS to test later in case it changes (write down the settings you use and always use the same ones)
4) run the Intel CPU diagnostic to make sure you get a PASS
https://downloadcenter.intel.com/download/19792/Intel-Processor-Diagnostic-Tool
5) Use CPUID's HWMonitor or other reliable tool to monitor the CPU temp (CPU shouldn't throttle until closer to 100degC in desktop, though laptops can set their own temperatures)
*Run any game and monitor both the CPU and GPU temps (probably can do CPU as well as GPU with MSI Afterburner)
OTHER:
There are settings for WALL POWER vs BATTERY too in I think the Power Options section that relate to battery life so it's possible that may be going on.
I really don't know how you tell if it's overheating since it will throttle itself automatically, though I don't think they usually throttle the CPU on laptops until they are somewhere in the 80degC to 85degC range (not counting POWER option settings for battery that is)