you can echo the percentage like this:

battatm=$(sysctl -n hw.sensors.acpibat0.amphour3 | sed s/.A.*//)
battfull=$(sysctl -n hw.sensors.acpibat0.amphour0 | sed s/.A.*//)
load=`echo "${battatm} / ${battfull} * 100" | bc`
echo ${load}