ftp://sipb.mit.edu/pub/netbsd/xbattery.tar.gz has an xforms application
for monitoring the battery charge state within X11.

Note that you may need to change <machine/apmvar.h> to <machine/apm.h>
(I'm renaming it from the latter to the former, but haven't put together
replacement diffs yet.)

(you can get the xforms toolkit from within
ftp://bloch.phys.uwm.edu/pub/xforms/)

==John