navigator.getBattery cannot be found

I made a program that would list the battery level and charging into a div. My code is below. For some reason, when I run it, it tells me that navigator.getBattery is not a function. How can I fix this?

function batttick() {
  navigator.getBattery().then( a=>{
    let m = ""
    let c = ""
    m = battery.level * 100 + "%"
  
    if(a.charging) {
      m+=" ⚡";
      c = "green";
    }
    console.log(c, m);
    document.getElementById("batt").innerHTML = m;
    document.getElementById("batt").style.color = c;
    })
} 
batttick()

You had an issue where you were using a variable a but were referencing battery. See my edits and working demo:

function batttick() {
  navigator.getBattery().then(battery => {
    let m = ""
    let c = ""
    m = battery.level * 100 + "%"

    if (battery.charging) {
      m += " ⚡";
      c = "green";
    }
    console.log(c, m);
    document.getElementById("batt").innerHTML = m;
    document.getElementById("batt").style.color = c;
  })
}
batttick()

<div id="batt"></div>