Alternative for navigator.getBattery() of battery api?

What should I use instead of navigator.getBattery(), as it is not working?

I am working on a chrome extension and with this what I want to do is –

function toggleBatterySaver(enable) {
  if (enable) {
      navigator.getBattery().then(battery => {
          if (battery.level < 0.2) {
              chrome.power.requestKeepAwake("system");
          }
      });
  } else {
      chrome.power.releaseKeepAwake();
  }
}

It is throwing an error:
navigator.getBattery() is not a function.