Thanks. I didn't know SBS was the particular kernel module responsible for this. However, lsmod reports it's loaded by default in my stock Arch kernel and I assume it has always been.

I have never been able to get events through acpi_listen when the battery reaches particular thresholds. Thus, udev rules for critical battery levels never work.

Any ideas why this is not working? I'm using a MBA 11 inch late 2012. Possibly the most Linux-compatible Mac machine ever. All stock Intel hardware.