How to create a Legend in UIextras?

Hello,

I created some small calculator/plotter, but I would like to add a legend to the plot, which does not work:

Here is a working example, just look for the commented section:

function travel_time_slider()

    close(findobj('tag', 'travel_time_slider'))

    f = figure('Tag', 'travel_time_slider', 'Position', [ 680   307   560   791]);
    handles.Figure = f ;
    
    vbox = uiextras.VBox( 'Parent', f, 'Padding', 15);
    handles.vbox = vbox;
    handles.axes = axes('Parent', vbox);
    [x, ladezeit, fahrzeit, gesamt, n, l, kW, kWh] = init_plot() ;
    
    handles.ladezeit = plot(x, ladezeit, 'DisplayName', sprintf('Total charging time (%4.2f min per charge)', l*60), 'linewidth', 2); grid on, hold on
    handles.fahrzeit = plot(x, fahrzeit, 'DisplayName', sprintf('Driving time for %g km', n) , 'linewidth', 2) ;
    handles.gesamt   = plot(x, gesamt, 'DisplayName', 'Sum' , 'linewidth', 2) ;
    title(sprintf('Travel time for %d km with %d kW charger and %d kWh charge', n, kW, kWh))
    xlabel('Velocity [km/h]')
    ylabel('Travel time [h]')
    ylim([0 20])
    
    %
    %
    % THIS PARD DOES NOT WORK
    %
    legend(handles.axes, 'location', 'north')
    %
    % % COMMENT IT OUT AND IT'LL WORK WITHOUT A LEGEND
    %
    %
    
    handles.slider_km = uicontrol('Parent', vbox, 'Style', 'slider',...
        'Min',100,'Max',2000,'Value',1000,...
        'Callback', @draw);
    handles.text_km = uicontrol('Parent', vbox, 'Style', 'text',...
        'FontSize', 14, 'FontWeight', 'bold', ...
        'String','Driving distance: 1000 km');
    
    handles.slider_kWh = uicontrol('Parent', vbox, 'Style', 'slider',...
        'Min',20,'Max',200,'Value',50,...
        'Callback', @draw);
    handles.text_kWh = uicontrol('Parent', vbox, 'Style', 'text',...
        'FontSize', 14, 'FontWeight', 'bold', ...
        'String','Electric battery charge: 50 kWh');
    
    handles.slider_kW = uicontrol('Parent', vbox, 'Style', 'slider',...
        'Min',20,'Max',400,'Value',50,...
        'Callback', @draw);
    
    handles.text_kW = uicontrol('Parent', vbox, 'Style', 'text',...
        'FontSize', 14, 'FontWeight', 'bold', ...
        'String','charger power: 50 kW');
    
    set(vbox, 'Sizes', [-1 20 25 20 25 20 25]) ;
    
    guidata(f, handles)

end

function [x, ladezeit, fahrzeit, gesamt, n, l, kW, kWh] = init_plot(n, kWh, kW)

    p = polyfit([80 120 200], [15 20 65], 2) ;
    x = linspace(100,200);

    if ~exist('n', 'var')
        n = 1000 ; % Kilometer 
    end
    if ~exist('kWh', 'var')
        kWh = 50 ; % Akkukapazität
    end
    if ~exist('kW', 'var')
        kW = 120 ; % Ladeleistung
    end
    
    l = kWh / kW ;  % Ladezeit

    ladezeit = (ceil(n ./ (kWh ./ polyval(p, x) * 100))-1) * l ;
    fahrzeit = n ./ x ;
    gesamt = fahrzeit + ladezeit ;

end

function draw(hObject, ~)
    handles = guidata(hObject) ;
    n = handles.slider_km.Value ;
    kWh = handles.slider_kWh.Value ;
    kW = handles.slider_kW.Value ;
    
    [x, ladezeit, fahrzeit, gesamt, n] = init_plot(n, kWh, kW) ;
    handles.gesamt.XData = x ; handles.gesamt.YData = gesamt;
    handles.ladezeit.XData = x ; handles.ladezeit.YData = ladezeit;
    handles.fahrzeit.XData = x ; handles.fahrzeit.YData = fahrzeit;
    
    title(sprintf('Travel time for %d km with %3.0f kW charger and %3.0f kWh charge', n, kW, kWh))
    handles.text_kWh.String = sprintf('Electric battery charge: %5.2f kWh', kWh) ;
    handles.text_kW.String = sprintf('charger power: %3.0f kW', kW) ;
    handles.text_km.String = sprintf('Driving distance: %4.0f km', n) ;
    
end

How can I make it work with a legend?