I've got a Surface Pro 4. It was great for the first year or so, when I was using it as a tablet on the couch for browsing, reading, and as a digital scratchpad.
I then got an iPad via a ridiculously good deal from Comcast (128 GB 6th generation (which was the latest generation at the time) for $120. The iPad took over most browsing, reading, and scratchpad duties, with the SP4 just getting occasional use when I needed something more general than the iPad.
What I noticed when the SP4 went from daily use to weekly or so is that the battery would always be low when I went to use it. Charge it up fully and shut it down...and a week later it needs charging again.
I believe that is because shut down is really some kind of sleep or hibernate. I've tried disabling all of those, and fast start. I've tried shutting down from the start menu, with and without the modifiers that are supposed to make it really shut down. I've tried command line commands that are supposed to really shut it down. I've tried shutting down from the BIOS.
But no matter what I do it consumes significant power while off. If I leave it on the charger so that it will be ready when I need it, it seems to charge to full, then stop charging until the battery drains a bit, and then repeats that cycles.
The result is after a couple years of sporadic use, the battery was degraded enough that now just using it for light browsing I'm lucky if I get 30 minutes of battery time. So now it is pretty much relegated to only being usable when hooked to external power.
I'm never buying another Surface product. And I'm not buying any Windows laptops or tablets unless there is some reasonable way to definitely turn them all the way off and have them stay that way.