Earlier quoted context omitted.
It requires lots of manual control but from my experience I can match or exceed battery life in comparison to running windows, with some tweaking. Out of the box it was terrible as well.
What did you adjust?
Two of my last five laptops were macs, three linux boxes, if you consider corporate laptops as "mine". One of the three linux laptops just worked beautifully (wrt. battery and other driver issues), one didn't at all, and one worked poorly until I installed some software that shouldn't matter for battery lifetime, and since then it's had excellent battery management. There was a long list of dependencies, so I suspect that the software I installed depended on a package that solved whatever the problem was.
You may chance to buy hardware where someone really has tested and fixed linux. Or you may get something else.
FYI: The two good ones are some Huawei thing that weighs 1.3kg and a GPD P2 Max, a tiny toy, really portable, https://rant.gulbrandsen.priv.no/hardware/attovax