Code

Provides information about the battery charge level of the host device and fires events when the level or charging state changes. Useful for adapting app behaviour — such as reducing network activity or disabling resource-intensive features — when battery is low.

MDN Reference

Key Interface — BatteryManager

• navigator.getBattery() — Returns a Promise<BatteryManager>.
• BatteryManager.charging — true if the battery is currently charging.
• BatteryManager.level — Battery level as a value between 0.0 and 1.0.
• BatteryManager.chargingTime — Seconds until fully charged, or 0 if already full.
• BatteryManager.dischargingTime — Seconds until battery is empty, or Infinity if charging.

Battery Events

Example — Read battery status

const battery = await navigator.getBattery();

console.log('Charging:', battery.charging);
console.log('Level:', Math.round(battery.level * 100) + '%');
console.log('Charging time:', battery.chargingTime, 'seconds');
console.log('Discharging time:', battery.dischargingTime, 'seconds');

Example — Adapt behaviour on low battery

Listen for level changes and reduce polling or disable animations when the battery drops below a threshold.

const battery = await navigator.getBattery();

function checkBattery() {
  if (!battery.charging && battery.level < 0.2) {
    console.warn('Low battery — entering power-save mode');
    reduceSyncFrequency();
    pauseBackgroundAnimations();
  }
}

battery.addEventListener('levelchange', checkBattery);
battery.addEventListener('chargingchange', checkBattery);

checkBattery(); // run immediately on load