Battery API in JavaScript: Monitoring Device Battery Status

The Battery API in JavaScript is a useful interface that allows web developers to access and monitor the status of a device's battery. This API provides information such as battery level, charging status, and whether the device is plugged in or running on battery power. By utilizing the Battery API, web applications can optimize their behavior based on the device's battery status, enhancing user experience and conserving energy. In this article, we'll explore what the Battery API is, its benefits, when to use it, and some practical use cases.

What is the Battery API?

The Battery API is a JavaScript API that provides information about the device's battery status and allows developers to respond to changes in that status. It is primarily used to retrieve information related to battery charge level, charging status, and battery discharging time.

Benefits of the Battery API

User Experience Enhancement

By accessing battery status information, web applications can adapt their behavior to conserve power when the device is running on battery or provide enhanced features when the device is plugged in and charging.

Energy Efficiency

Utilizing battery status information, web apps can optimize resource-intensive operations to reduce energy consumption and extend device battery life.

Real-Time Updates

The API provides real-time updates on battery status changes, allowing web apps to respond immediately to changes such as unplugging the device or low battery levels.

Cross-Platform Compatibility

The Battery API is supported by many modern browsers, making it a reliable choice for cross-platform development.

When to Use the Battery API

Consider using the Battery API when your web application needs to:

  1. Provide Power-Aware Features

    Adapt your application's features and behavior based on whether the device is running on battery power, charging, or fully charged.

  2. Conserve Battery Life

    Optimize resource-intensive operations when the device is running on battery power to reduce energy consumption and prolong battery life.

  3. Display Battery Status

    Show battery-related information to users, such as the current battery level or estimated time until the battery is fully charged.

  4. Trigger Actions on Battery Events

    Execute specific actions when the battery status changes, such as displaying a low battery warning or pausing resource-intensive tasks.

Practical Use Cases

  1. Low Battery Alert

    You can use the Battery API to trigger a low battery alert when the device's battery level drops below a certain threshold, prompting users to conserve energy or plug in their device.

  2. Energy-Efficient Animations

    Web applications can adjust the intensity and frequency of animations based on the device's battery status to reduce the drain on the battery.

  3. Background Process Management

    Optimize background processes, such as syncing data or sending notifications, to occur less frequently when the device is running on battery power to conserve energy.

  4. Dynamic Resource Loading

    Load high-resolution images or resource-intensive content only when the device is charging or when the battery level is above a certain threshold, improving performance and energy efficiency.

Basic Example: Monitoring Battery Status

Here's a simple example of how to use the Battery API to monitor the battery status of a device:

<!DOCTYPE html>
<html lang="en">
    <meta charset="UTF-8">
    <title>Battery Time Estimation</title>
    <h1>Battery Time Estimation</h1>
    <div>Time Remaining: <span id="timeRemaining">Calculating...</span></div>

    <script>navigator.getBattery().then(function(battery) {
    function updateTimeRemaining() {
        let time = battery.dischargingTime;
        if (battery.chargingTime !== Infinity) {
            time = battery.chargingTime;
            document.getElementById('timeRemaining').textContent = `Charging, time left: ${time/3600} hours`;
        } else if (time === Infinity) {
            document.getElementById('timeRemaining').textContent = 'Plugged in, not charging';
        } else {
            document.getElementById('timeRemaining').textContent = `Time remaining: ${time/3600} hours`;


    battery.addEventListener('chargingchange', updateTimeRemaining);
    battery.addEventListener('levelchange', updateTimeRemaining);
    battery.addEventListener('chargingtimechange', updateTimeRemaining);
    battery.addEventListener('dischargingtimechange', updateTimeRemaining);

How It Works:

  • Time Estimation: The script checks whether the battery is charging or discharging and displays an estimated time until the battery is fully charged or depleted.
  • Event Listeners: It updates the display in real-time as the battery status changes.

This example helps to illustrate how the Battery API can provide detailed insights into battery usage, including time estimates, which can be particularly useful for mobile devices and laptops in managing power consumption and planning usage.


The Battery API in JavaScript provides web developers with a valuable tool to access and respond to the battery status of user devices. By utilizing this API, web applications can enhance user experience, conserve battery life, and optimize energy efficiency. Whether you're building a mobile app, a web game, or any application that runs on battery-powered devices, the Battery API empowers you to create power-aware and user-friendly web experiences.

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