The logic for the detection of the battery/AC line was not completely correct
for FreeBSD. Launching conky on console shows the following:

Cannot read sysctl "hw.acpi.battery.time"
Cannot read sysctl "hw.acpi.battery.life"
Cannot read sysctl "hw.acpi.battery.state"
Cannot read sysctl "hw.acpi.acline"
Unknown battery state 8!

In a PC, the hw.acpi.battery MIB does not exist.
Also, the hw.acpi.acline is only present if supported by the hardware.
In addition, some variables were used uninitialized and that causes strange
behavior: in a PC it showed it worked on battery and the % of charge was an
ridiculous big number.

This patch addresses the issue. It fixes the problem in the PC. It has also
being tested in a laptop running FreeBSD current plugin and unplugging the AC
line and also snatching the battery mercilessly to see if something breaks.