Quoting Jason Chu <jason@archlinux.org>:
From the release logs, IIRC, as of 2.6.21 the acpi stuff moves now from /proc/acpi to /sys. This is supposed to be work in progress, but the
stuff might be already affected. (I'm fishing here, I didn't check the
battery patches)
-T
Actually, I'm the one who has a problem with xfce, 2.6.21, and the battery monitor. Using 2.6.20 (with modules) it works but using 2.6.21 (with modules) it doesn't. The acpi command still works, but the panel battery monitor doesn't.
Someone else try it! Make me not look crazy! Hehehe, I doubt you're crazy, I said I'm fishing. I can try it on my testing laptop by tomorrow. That the acpi command still works is a hint that /proc/acpi/battery still exists and the battery-monitor uses a different method to read out information. But, glancing over the code, the battery-monitor uses a libacpi.c file reading from hard-coded /proc/acpi/... directory. Can you see if you still have a /proc/acpi/battery/BAT0 directory and post the output of cat /proc/acpi/battery/BAT0/* please?
-T