Update battery.plugin to check for acpi existence

plugins/battery.plugin.bash

@@ -1,6 +1,8 @@
 #!/bin/bash
-
+# pmset -g batt
 battery_percentage(){
+  if command_exists acpi;
+  then
     local ACPI_OUTPUT=$(acpi -b)
     case $ACPI_OUTPUT in
       *" Unknown"*) 
@@ -19,6 +21,9 @@ battery_percentage(){
         echo '-1'
         ;;
     esac
+  else
+    echo "no"
+  fi
 }
 
 battery_charge(){
@@ -34,6 +39,9 @@ battery_charge(){
   local BATTERY_PERC=$(battery_percentage)
 
   case $BATTERY_PERC in
+    no)
+      echo ""
+      ;;
     9*)
       echo "${FULL_COLOR}${F_C}${F_C}${F_C}${F_C}${F_C}${normal}"
       ;;