Battery Status Checker

How to check your battery

1. Open this page in Chrome, Edge, Opera or another Chromium-based browser. The status is read as soon as the page loads; press Read battery status to refresh it at any time.
2. Read the Level, the State (Charging, On battery or Full (plugged in)) and the two times the operating system estimates: Time to full and Time remaining.
3. Keep the tab open while you work. Every time the level moves by one step, a row is added to Level changes, and plugging or unplugging the charger is logged too.
4. After two level changes spanning at least 30 seconds, Observed rate shows how fast the battery is really draining or charging, in % per hour, and Estimate from rate turns it into a time to empty or to full.

Watching for shows how long the page has been monitoring. The longer you leave it, the more reliable the observed rate becomes.

What the numbers mean

The browser gets four values from the operating system through the Battery Status API: the level (0 to 100 %), whether a charger is connected, the seconds until the battery is full and the seconds until it is empty. When the system has no estimate yet, it reports “infinity”; this tool shows that as Unknown. That is normal just after plugging in or unplugging, and some systems never provide the times at all.

The Observed rate is computed by this tool, not by the system. It only uses the moments when the level actually changed, since the latest plug or unplug. The first reading can fall anywhere inside a 1 % step, so the rate is measured from the first change to the last one:

rate (%/h) = (last level − first level) ÷ elapsed hours between those two changes

While discharging, the time to empty is the current level divided by the rate; while charging, the time to full is the missing percentage divided by the rate. Chromium rounds the level to whole percents to limit fingerprinting, so a laptop draining at 10 %/h only produces a new step every six minutes. Give it 15 to 30 minutes for a meaningful figure.

Tips for an honest measurement

• Keep your usual workload: a video call, a game or a compile will drain the battery several times faster than reading a web page.
• Screen brightness and the power mode (battery saver, best performance) change the rate a lot. Compare runs with the same settings.
• Charging slows down above about 80 %: lithium-ion batteries switch from constant current to constant voltage, so the charge rate falls as the battery fills.
• A drain rate much higher than when the laptop was new is a sign of battery wear. The operating system’s battery report gives the design and full-charge capacities.

Browser support

Only Chromium-based browsers still expose the API: Chrome, Edge, Opera, Brave, Vivaldi and Samsung Internet. Firefox and Safari removed it because the precise level and times could be combined to track visitors across sites. In those browsers the tool displays a message instead of results. On a desktop computer without a battery, Chrome reports a full battery on mains power.