something like https://wiki.archlinux.org/index.php/Power_management#SATA_Active_Link_Power_Management

Following Guido's link, I ran

$  cat /sys/class/scsi_host/host*/link_power_management_policy
med_power_with_dipm
med_power_with_dipm

Which is, AIUI, the desired default setting for ALPM. It is possible that our kernel in Byzantium already has this as the as the default setting but more investigation is needed.

Oh good!
Or also not so good, because then I wonder what people do with their laptops not getting more battery life... hmm...

@jeremiah.foster could you check if min_power makes a difference? It seems to save 0.5W here things are fluctuating quite a bit so a longer test would be good.

So how do we do this test in a way that produces useful data? Do we run it at two different settings on two laptops concurrently? Or should I measure battery level over time at specific intervals with each setting on the same device?

Do you have an AC power meter? That's what I used... let the system sit there idle, battery fully charged, look at power consumption. Then just change _one_ thing at a time, let it settle and become idle again, measure again.

I have such a tool you can plg between the wall socket and the laptop power cord which displays Watt directly.

@jeremiah.foster powetop shows the amount of power drawn from the battery as a rough indicator

I don't have a power meter but I will use powertop. :-)

This IIRC does not work with the Librem laptops since these do not measure the energy properly, instead just estimate based on discharge rate. And even if, it is really rough (even Thinkpads do a pretty bad job at it).

Something like this maybe:

https://www.amazon.com/Upgraded-Consumption-Electricity-Overload-Protection/dp/B07P8M7N9F/ref=sr_1_6?dchild=1&keywords=wall+plug+power+meter&qid=1602695886&sr=8-6