JSFiddle - React, Tailwind, and code Playground

HTML

<!-- 

ACHTUNG
navgator.getBattery funktioniert nur in Chromium-Basierten Browsern.

-->

<span id="akku"></span>

JavaScript

var akku;
 navigator.getBattery().then(function(battery) {
   var akku = battery.level * 100;
 });
document.getElementById('akku').innerHTML = akku;