Get Current Window Handle

I would suggest your EA writes (Comment() or test-lable) the no. of its chart (not ChartID) on the screen and sets a global-variable with a informative name and sets the value to the no. of its chart. 

(Not tested!)

int findChart(){
   long myChart = ChartID(),
        nxChart = ChartFirst();
   if (nxChart == myChart) return(1);
   int ret = 2;
   while(nxChart!=-1) {//beyond last chart
      nxChart = ChartNext(nxChart);
      if (myChart == nxChart) return(ret);
      ret++;
   }
   return(-1); // not found
}

Don't set the value to the Chart-ID! Its a long value which will be converted to a double and if you re-convert it back to a long value again this value will differ from the original ChartID!!

This will not work 100%, but it gave me the idea: Use CHART_WINDOW_HANDLE combined with looping of the charts!

Thanks! 

ChartGetInteger(0,CHART_WINDOW_HANDLE);

Thank You. This code was very good to me.