How does conky determine the battery usage? does this system use
apm(4) or
acpi(4)? do you use
apmd(8)? what's the output of apm?
If you're using ACPI, look in your dmesg and see if acpibat* attaches.. if so, the sysctl members
hw.sensors.acpibat0.* should exist.
It's difficult to get battery usage information portability across operating systems, but with a little scripting you can probably pull something off that can display battery usage.