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%?
I would instead look into the firmware settings. Dell has good Linux support.