What be wondered, and is probably.more likely than nit, is that with these builds, Microsoft is probably running diagnostic tools in the background that we don't get to see, as if the builds are self reporting as part of the telemetry data Microsoft collects. I think this would contribute to poorer battery life and warmer devices.
Ding ding ding! You've got it. As someone with 30+ years experience as a programmer/developer, the best way to find the bugs in something very complex is to have extra code execution put in that can be later removed. Then, as the software is run, it will compile reports showing how the different areas of the software is performing. This makes it easier to locate the problem areas and identify what to do about them to get them fixed. Yes, it causes lots of extra CPU cycles, which introduces extra heat and power requirements.
So, people, THIS is why battery life is always bad on these early Insider builds, as it has been from the beginning of the insider program way back when. It is also why battery life improves dramatically, seemingly overnight almost, once bugs are almost completely gone and it is nearing release. There are "conditional" statements that can be placed around the debug code. Then a variable can be defined at the beginning of the code stating something like, "DEBUG_MODE = ON". Switch that to OFF, and it will no longer compile with those lines of code and all the extra CPU cycles will immediately disappear, yet they can turn it back on for the next internal build.
I tried to put it into layman terms, so other developers, please don't pick on the syntax of the above DEBUG_MODE, as it is meant as a teaching tool to non-programmers.
Hope it helps explain a bit.
And, developers, if you aren't using these types of techniques in your code, you should be. It saves a LOT of headaches and hassles, and helps you to fix things much more quickly.