How to compare charging with the screen on and off

Does your phone or laptop seem to charge more slowly while you use it? A bright screen and active apps draw power, but the charger, battery level, and temperature also affect how quickly the percentage rises.

Use the Charger & Cable Test to compare charging speed in percent per minute. A browser may pause its measurements when the screen sleeps, so you may need to compare the battery percentage before and after a timed screen-off period as well.

Compare charging with the screen on and off

Open the Charger & Cable Test on the device you want to check. The test appears only on devices whose browser reports battery information. Confirm that the device is charging and note its battery percentage.
Keep the same charger, cable, outlet, and device for both parts. Start at a similar battery level each time, ideally within a few percentage points, and avoid testing near full charge, when charging often slows down.
For the screen-on measurement, leave the screen at a fixed brightness and keep the device mostly idle. Watch the test's charging speed and note the rate after it has had time to settle. If the rate keeps changing, record the time and battery percentage too.
For the screen-off measurement, note the battery percentage and the time, then turn off the display or lock the device. Leave it charging for 15 to 30 minutes, then wake it and note the new percentage. Use a longer interval if the battery percentage barely changes.
Compare the results in percent per minute. For the screen-off period, divide the percentage-point increase by the number of minutes. For example, a rise from 40% to 44% in 20 minutes is 0.2 percentage points per minute.

On some phones and computers, the browser stops updating when the display turns off. Do not assume the test measured that period in the background. The before-and-after battery percentage is a practical comparison, but it is less precise because the displayed percentage is rounded. For context on this unit, see what battery percentage per minute can tell you.

What the result means

The screen-on rate is lower

The device is using some of the incoming power while you use it. A bright display, video playback, navigation, games, or a busy connection can all increase power use. The battery may still be charging normally, even if less of that power is available to raise its percentage.

The rates are close

Your charger may have enough capacity to run the screen and charge the battery at nearly the same rate as when the screen is off. A small difference can also be hidden by percentage rounding, especially during a short comparison.

The screen-off result looks slower or shows no increase

This does not prove that the screen-off state prevents charging. The browser may have paused, the percentage may not have crossed the next whole number yet, or the device may have changed its charging rate because of heat or battery level. Repeat the comparison over a longer interval before drawing a conclusion.

The readings vary from one attempt to another

Charging speed is not constant. Batteries often charge more slowly as they get fuller, and a warm device may reduce charging to protect itself. Different starting percentages, brightness levels, background tasks, or cable connections can make two readings hard to compare.

Make the comparison fair

Match the starting charge. Begin both measurements at nearly the same percentage. Avoid comparing a low battery with a nearly full one, because the charging rate can change as the battery fills.
Keep the charging setup unchanged. Use the same cable, charger, outlet, and port. Do not compare a wall charger in one test with a computer USB port in the other.
Keep the device cool and idle. Remove a thick case if the device feels warm, stop games and video, and leave background downloads alone. Do not run a demanding app only during the screen-on test.
Set a consistent screen brightness. Use the same brightness and screen content for each screen-on run. A bright white screen can use more power than a dim screen.
Prevent the computer from sleeping during a display-off test. On Windows 11, open Settings › System › Power & battery › Screen and sleep and make sure the computer will not go to sleep during the timed interval. On macOS, check System Settings › Lock Screen for the display-off timing options. A sleeping computer may pause the browser or change power use beyond the screen itself.
Use a timer and repeat the pair. On a phone, the screen timeout is usually under Settings › Display; on iPhone, check Settings › Display & Brightness › Auto-Lock. Menu names vary by Android model. If the result is close, repeat the comparison rather than treating a one-point change as a definite difference.

When to suspect the charger or cable

If the device barely gains charge in both conditions, test with a known-good charger and cable that are suitable for that device. Check that the connector fits securely and that the charging port is free of visible debris. Do not insert metal tools into the port.

If charging repeatedly stops, the connector gets unusually hot, or you see damage to the cable or charger, stop using that part. A browser test measures a change in battery percentage, not electrical safety or the charger's exact wattage. For safety limits, read what charging tests cannot tell you about electrical safety.

Why the browser result is only an estimate

Percent per minute describes how quickly the reported battery percentage changes. It is not the same as watts, and it cannot show exactly how much power the screen uses. Battery percentages are rounded, while browsers can restrict access to battery information or pause work when a device is locked. Use the same device and conditions to compare trends, not to certify a charger.

Nothing you record is uploaded, and this test does not need a recording. The charging measurements depend on battery information reported by your device and browser.