How do I test my laptop's battery drain?

Charge it, unplug it, set the brightness you use, choose a load above and start. After ten minutes or more the page shows the drain in percent an hour and an estimated runtime.

How accurate is a browser battery test?

As accurate as the 1 percent steps the system reports allow. Longer runs are more accurate; the page shows the range one step of rounding would give.

Can it measure battery health?

No. Health is the full-charge capacity against the design capacity, which browsers do not share. A faster drain than before is a hint; the system's battery report is the measurement.

Why did the test stop?

The charger was plugged in, or the page was closed. A drain cannot be measured while charging.

Is the drain on video the same as on a streaming site?

Close, not the same. The page decodes its own clip at 30 frames a second; a streaming site adds the network, its own player and often a higher resolution.

Free · Chrome and Edge · Ten minutes or more

Battery drain test. Percent an hour, measured.

Unplug the laptop, choose a load (idle, video or the processor) and leave the page running. It records the battery level the browser reports against time, works out the drain in percent an hour from the moments the level changed, and extrapolates a runtime, labelled as an estimate. It stops by itself if the charger goes in. The level moves in 1 percent steps, so it needs at least ten minutes.

One check · Ten minutes or more

Asks for: A laptop on battery, in Chrome or Edge. It runs in its own window and nothing leaves this page.

In short

Battery drain test: the answer first

A laptop battery drain test records the charge level against time under a fixed load and works out how fast it falls. This one runs in Chrome or Edge, with idle, video or processor load, and gives percent an hour from the moments the level changed, plus a straight-line runtime estimate labelled as one. It needs ten minutes or more, because the level moves in 1 percent steps.

Reading your result

Percent an hour: The measured figure, with the range one step of rounding either way would give. Longer runs narrow it.
Estimated runtime: The level over the rate, in a straight line. Batteries do not drain in one, so treat it as a guide.
Compare like with like: The same load at the same brightness and power mode, before and after a change, is the comparison that means something.

What it measures

Measured here, not assumed.

Level against time: The Battery Status API's level, read every five seconds and whenever the browser reports a change, with the charging state.
Drain rate: Percentage points an hour from the first to the last change of level, so the rounding inside a step does not bias it, with the range allowing one step of rounding either way. At least ten minutes and two steps first (our starting values).
The load you chose: Idle: nothing. Video: a 1080p clip encoded on the page and decoded at 30 frames a second, or an animated canvas where the browser cannot decode one, labelled so. Processor: workers busy on every logical core but one.
Runtime, estimated: The current level, and a full charge, over the rate: a straight-line extrapolation, labelled as one.

If it fails

The usual failures, and what fixes each.

The drain is faster than it used to be: Run the same load at the same brightness as before. If it is still faster, look at wear: powercfg /batteryreport on Windows compares design and full-charge capacity.
Idle drain is high: Something is busy in the background. Check the task manager for processes using the processor, lower the brightness, and turn off keyboard lighting and unused radios.
The laptop is slow on battery: Many laptops limit power on battery. The laptop stress test, run once on battery and once plugged in, measures how much.

Where a browser stops

What it cannot tell you.

Battery wear, capacity, cycle count, watts and temperature. Browsers do not share them; powercfg /batteryreport on Windows and System Information on a Mac do.
Better than 1 percent. The system reports the level in 1 percent steps and rounds it its own way.
A straight line. Batteries do not drain in one, and systems hold back the last few percent.
Firefox and Safari, which do not share the battery level.
Brightness and the power mode, which change the rate and which the page cannot read; set them before you start.

Privacy

Nothing leaves this page.

The camera and microphone are read on this page and stopped as soon as they have been measured. The clip you can play back lives in the browser's memory and is discarded when you leave. The location check discards the position. The internet test sends random bytes to this site and nothing else. The result is stored nowhere unless you ask for it by email, and then only the fact that an email was sent is kept.

The privacy policy

Questions

Battery drain test, answered

How do I test my laptop's battery drain?: Charge it, unplug it, set the brightness you use, choose a load above and start. After ten minutes or more the page shows the drain in percent an hour and an estimated runtime.
How accurate is a browser battery test?: As accurate as the 1 percent steps the system reports allow. Longer runs are more accurate; the page shows the range one step of rounding would give.
Can it measure battery health?: No. Health is the full-charge capacity against the design capacity, which browsers do not share. A faster drain than before is a hint; the system's battery report is the measurement.
Why did the test stop?: The charger was plugged in, or the page was closed. A drain cannot be measured while charging.
Is the drain on video the same as on a streaming site?: Close, not the same. The page decodes its own clip at 30 frames a second; a streaming site adds the network, its own player and often a higher resolution.

Then test the machine itself. A free stress test, in the same browser.

Run the stress test How we measure