google.maps.event.addListener(marker, 'click', function() {
            infowindow.open(map1, marker);
        });

infoWindow = new google.maps.InfoWindow; //static infoWindow for all your markers
google.maps.event.addDomListener(window, 'load', function() {
   //create your markers here
   google.maps.event.addListener(marker, 'click', function() {
               infoWindow.open(map1, marker); //take care with case-sensitiveness
          });
});