navigator.getBattery() read time

gistfile1.txt

http://jsbin.com/zibaraju/1/edit

<div></div>
<script>
  var div = document.querySelector('div');
  
  setInterval(function() {
  var t0 = performance.now();

  navigator.getBattery().then(function() {
    var t1 = performance.now();
    div.innerHTML += (t1 - t0) + " ms<br>";
  }, function() {
    console.log('error');
  });
}, 1000);
</script>

Reading the navigator.getBattery() every 1000ms (including the very first read)
--------------------------------------------------------------------------

// Chrome Desktop - 38.0.2109.0 (Official Build 286623) canary

1.9339999998919666 ms
0.5879999953322113 ms
0.5550000350922346 ms
0.2690000110305846 ms
0.23200002033263445 ms
0.7070000283420086 ms
0.3179999766871333 ms

// Chrome Android - 38 dev

3.273999987868592 ms
0.6850000063423067 ms
5.814000003738329 ms
1.564000005600974 ms
0.13800000306218863 ms
0.7790000236127526 ms
0.7120000082068145 ms