if [[ $(acpi 2&>/dev/null | grep -c '^Battery.*Discharging') -gt 0 ]] ; then
   function battery_pct_remaining() { echo "$(acpi | cut -f2 -d ',' | tr -cd '[:digit:]')" }
   function battery_time_remaining() { echo $(acpi | cut -f3 -d ',') }
   function battery_pct_prompt() {
     b=$(battery_pct_remaining)
     if [ $b -gt 50 ] ; then
       color='green'
     elif [ $b -gt 20 ] ; then
       color='yellow'
     else
       color='red'
     fi
     echo "%{$fg[$color]%}[$(battery_pct_remaining)%%]%{$reset_color%}"
   }
 else
   error_msg='no battery'
   function battery_pct_remaining() { echo $error_msg }
   function battery_time_remaining() { echo $error_msg }
   function battery_pct_prompt() { echo '' }
 fi