You know Andrew7783, it may all sound a bit confusing but
you may have started one of the most important threads out there. No matter what generation model of Surface tablet or laptop (even Book) model you have, they all have the exact same power management system. You fix one, you fix all. The only two machines
that are different are the Surface Hub and Surface Studio which are A/C powered only.
What may be confusing is the RTM and Windows Insider Builds but this is where the experiment of the builds come in handy. If an experimental firmware update is either built into a build or comes separate in a build and fixes an issue, this is an indicator
to Microsoft that they can say "hey, maybe we finally got it" and can test it on an RTM build to see if they get the same result. If it works, then they can release it to those with RTM machines as a firmware update (can also be buried in an Accumulative
Update) and fix everybody's problem.
I personally think you started the most important thread on the entire forum because power management has been a thorn in the entire Surface series. This started a discussion and some came up with a 'fix' on their own and got good results but it is actually
in Microsoft's court to actually fix the problem.
I have been on my Surface Laptop (1st gen) right now with Build 18990 and had no power drop overnight and also been on battery for over an hour right now and the battery gauge says 87%. I never got a battery life like that before and would have been down
in the 60s. This newer firmware update (which was included within the build), seems to be doing the trick.
Good job on you to start this thread! A real good discussion is coming out on this.