You want to hide your main window, and then put up a different window and mark it as "transient", which means it's a menu or popup or something like that. The following works for me, though I don't have KDE.

Also, in some window managers (like fvwm), you can configure different window decorations for different window names. So you could have a config line like "Style BatteryMeter NoTitle" or something along those lines.

#!/usr/bin/perl -w

use strict;
use Tk;

use constant UPDATE_PERIOD => 30; # seconds
use constant METER_MAX_LEN => 500;
our $BatteryMeter;

sub set_meter_size
{
    my $percent_strength = shift;
    my $new_len = int $percent_strength * METER_MAX_LEN;
    $new_len = 1 if $new_len < 1;
    # Geometry format is WidthxHeight+OffsetFromLeft+OffsetFromTop
    $BatteryMeter->geometry("${new_len}x2+10+200");
}

sub update_battery_strength
{
    my $battery_strength = rand(); # instead of rand(), figure out you
+r
                                   # battery life
    set_meter_size($battery_strength);
}

my $main_window = MainWindow->new();
$main_window->withdraw();
$BatteryMeter = $main_window->Toplevel(-background => 'red');
$BatteryMeter->transient($main_window);

update_battery_strength();

$BatteryMeter->repeat(1000 * UPDATE_PERIOD, \&update_battery_strength)
+;

MainLoop();
[download]

Good luck!