Fix battery i3block

dot_config/i3blocks/scripts/executable_battery

@@ -24,12 +24,16 @@ my $short_text;
 my $bat_number = $ENV{BLOCK_INSTANCE} || 0;
 
 # read the first line of the "acpi" command output
-open (ACPI, "acpi -b | grep 'Battery $bat_number' |") or die;
+open (ACPI, "acpi -b 2>/dev/null| grep 'Battery $bat_number' |") or die;
 $acpi = <ACPI>;
 close(ACPI);
 
 # fail on unexpected output
-if ($acpi !~ /: (\w+), (\d+)%/) {
+if (not defined($acpi)) {
+    # don't print anything to stderr if there is no battery
+    exit(0);
+}
+elsif ($acpi !~ /: ([\w\s]+), (\d+)%/) {
 	die "$acpi\n";
 }