It turns out that the ACPI support on the Gateway laptop is all fux0red under Linux because Gateway ships these machines with a fux0red BIOS. Of course, they also ship compensating Windows drivers, effectively rendering the power-management, battery monitoring, etc. capabilities of the machine Windows-only. Thanks guys.
Specifically, the BIOS lacks an ECDT, so parsing the DSDT during ACPI setup time dies violently as there's no way to access the embedded controller region. I have been hax0ring the kernel trying to fake an ECDT but without too much success: I have (what I believe to be) a fake ECDT that I plug in, but the kernel rejects it with:
tbget-0292: * Info: Table [ECDT] replaced by host OS tbrsdt-0227: * Error: Invalid signature where RSDP indicates RSDT/XSDT should be located
which I really understand. And unfortunately the acpi-devel list is only sporadically useful—though I can't say I blame them, as this is a hardware issue.
But it sure would be awfully nice to be able to see how much battery juice was remaining....#