Fix battery usage if the first battery doesn't begin with 0

fetch

@@ -1343,7 +1343,7 @@ getdisk () {
 getbattery () {
     case "$os" in
         "Linux")
-            if [ -d "/sys/class/power_supply/BAT0" ]; then
+            if [ -d "/sys/class/power_supply" ]; then
                 # Set the index to the battery number.
                 case "$battery_num" in
                     "all") battery_num="*" index=0 ;;