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The Battery Status API, more often referred to as the Battery API, provides information about the system's battery charge level and lets you be notified by events that are sent when the battery level or charging status change. This can be used to adjust your app's resource usage to reduce battery drain when the battery is low, or to save changes before the battery runs out in order to prevent data loss.

The Battery Status API extends window.navigator with a navigator.getBattery() method returning a battery promise, which is resolved in a BatteryManager object providing also some new events you can handle to monitor the battery status.

Example

In this example, we watch for changes both to the charging status (whether or not we're plugged in and charging) and for changes to the battery level and timing. This is done by listening for the chargingchange, levelchange, chargingtimechange, dischargingtimechange events.

navigator.getBattery().then(function(battery) {
  function updateAllBatteryInfo(){
    updateChargeInfo();
    updateLevelInfo();
    updateChargingInfo();
    updateDischargingInfo();
  }
  updateAllBatteryInfo();

  battery.addEventListener('chargingchange', function(){
    updateChargeInfo();
  });
  function updateChargeInfo(){
    console.log("Battery charging? "
                + (battery.charging ? "Yes" : "No"));
  }

  battery.addEventListener('levelchange', function(){
    updateLevelInfo();
  });
  function updateLevelInfo(){
    console.log("Battery level: "
                + battery.level * 100 + "%");
  }

  battery.addEventListener('chargingtimechange', function(){
    updateChargingInfo();
  });
  function updateChargingInfo(){
    console.log("Battery charging time: "
                 + battery.chargingTime + " seconds");
  }

  battery.addEventListener('dischargingtimechange', function(){
    updateDischargingInfo();
  });
  function updateDischargingInfo(){
    console.log("Battery discharging time: "
                 + battery.dischargingTime + " seconds");
  }

});

See also the example in the specification.

Specifications

Specification Status Comment
Battery Status API Candidate Recommendation Initial definition

Browser compatibility

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari
Basic support 39.0 10 (10) moz
16 (16)[1]
43 (43)[3]
No support 25 No support
Feature Android Android Webview Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile Chrome for Android
Basic support No support 40.0

10.0 (10) moz
16.0 (16)[1]
43 (43)[3]

No support 25[2] No support 42.0[2]

[1] Disabled by default in Firefox 10.0, but can be enabled setting the preference dom.battery.enabled to true. Starting with Firefox 11.0, mozBattery is enabled by default. The Battery API is currently supported on Android, Windows, and Linux with UPower installed. Support for MacOS is available starting with Gecko 18.0 (Firefox 18.0 / Thunderbird 18.0 / SeaMonkey 2.15). Firefox also provide support for the deprecated navigator.battery.

[2] Values for BatteryManager.chargingTime and BatteryManager.dischargingTime are always equal to Infinity.

[3] The new promise-based syntax for Navigator.getBattery() is supposed in Firefox 43 onwards.

See also

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