nikto93i7,
<!DOCTYPE HTML>
<html>
<head>
<title>Untitled</title>
<meta charset="utf-8">
</head>
<body>
<select id="charge_platform_car" class="option_menu_style_car" size="0" onchange="alert(this.value)">
<option class="car3_5">Charge 3.5t <span>32</span> kWh</option>
<option class="car3_5">Charge 3.5t <span>42</span> kWh</option>
<option class="car3_5">Charge 3.5t <span>52</span> kWh</option>
/**/
<option class="car5_5">Charge 5.5t <span>32</span> kWh</option>
<option class="car5_5">Charge 5.5t <span>42</span> kWh</option>
<option class="car5_5">Charge 5.5t <span>52</span> kWh</option>
/**/
<option class="car9_5">Charge 9.5t <span>52</span> kWh</option>
<option class="car9_5">Charge 9.5t <span>62</span> kWh</option>
/**/
<option class="car26">Charge 26t <span>60</span> kWh</option>
<option class="car26">Charge 26t <span>62</span> kWh</option>
</select>
<script>
var a = [].forEach.call( document.querySelectorAll('#charge_platform_car option'), function(el) {
el.value = el.text.match(/\d+(?=\s)/)
});
</script>
</body>
</html>