I have installed Linux Mint 22 in a DELL laptop with a buggy ACPI implementation (the kernel complains about it during boot). The laptop hangs if it goes to sleep (I tried various Linux distros/kernel-versions, the result is the same).
Because of that, I have disabled SLEEP in the firmware (latest version for that laptop btw). So basically, when you close the lid, nothing happens (it just locks the screen).
However, sometimes you might be in a hurry and you close the lid to do something else, and then you forget about it. The result would be for the battery to run dry, which eventually destroys the battery.
My question is: what would be the best way to setup an audible alarm if the battery reaches 20%?
The arch wiki has a udev rule that can automatically do something if the battery crosses a certain threshold: https://wiki.archlinux.org/title/Laptop#Hibernate_on_low_battery_level
No polling which is great. I always try to do stuff on an event driven basis where possible for efficiency reasons. Gotta test this out though, since your battery might not send events for every percent change.