function battery_size()
{
//shove values into variables
var load = document.forms[0].load.value;

var voltselect = document.forms[0].voltage.selectedIndex;
var voltage = document.forms[0].voltage.options[voltselect].value;

var dayselect = document.forms[0].days.selectedIndex;
var days = document.forms[0].days.options[dayselect].value;



//calculate result for 80pc dod
var result = load * days / 0.8 / voltage;
result = Math.round(result);

//validate

var verify = isNaN(result);
if (verify) {
	alert ("Enerji Tüketimi Rakam Olmalıdır");
	document.forms[0].load.focus();
	return false;
	};

// write result to form
document.forms[0].result.value = result;
}