Manufacturing probably way outshines the usage. And, the side-benefit of using old machines with say NetBSD or OpenBSD etc is that it makes people realize that they don't NEED new modern shiny hardware. I am still daily-driving a x220 on the road (it gets 99% of my stuff done) and at home I am using mostly a slightly upgraded T480. So a 15 year old and a 8 year old laptop. And power consumption wise, my T480 lasts about 17 hours on a charge. That is about same time I'd get out of a modern M3 MacBook Air.
With a bit less performance? Sure. But for my use-case it works. And more people realizing that might actually be a good thing.
T480 can hold 2 batteries. A swappable and an internal one. At least under FreeBSD the swappable alone gives about 10-11 hours on low brightness. The internal one carries the rest of the way.
I did replace the screen with a low power screen, which easily had the biggest impact on battery life.
I haven't tested the T480 under OpenBSD in a while, but my guess is that if I ran it with "apm -L", it would get close to the same numbers.
It's the Innolux IGZO Low-Power FHD Panel. There are similar ones or same on AliEpxress for example. Compared to the default FHD screen of the T480, The low power screen cuts the power consumption of the display by about 40%. While also having better contrast and brightness. Biggest power-saving upgrade for the T480.
With a bit less performance? Sure. But for my use-case it works. And more people realizing that might actually be a good thing.