Why battery charge rate varies between tests

You use the same charger, but one test reports a faster charge rate than another. That does not automatically mean the charger or cable is failing. Battery charging changes as the device warms up, gets closer to full, or uses power while plugged in.

The Charger & Cable Test compares charging speed in percent per minute. Here is how to run a fair comparison and make sense of changing results.

Compare the charger and cable fairly

Open the Charger & Cable Test on the device you want to check. The test is available when your browser reports battery information.
Use a similar starting charge for each test. A range around 20 to 50 percent is more useful than testing near full, when charging commonly slows down.
Keep the device idle while it charges. Turn off the screen if practical, close demanding apps, and avoid changing settings or using the device during one test but not the other.
Test one change at a time. Keep the charger and outlet the same while swapping cables, then keep the cable the same while swapping chargers. Let each test run long enough for the reported level to change.

For a second view of the battery state, open the Battery Meter. It shows charge level and charging state when that information is available. It does not measure electrical power either, so use it to check whether the device is charging, not as a wattmeter.

What the result means

The rate changes during one test

This is common. Charging is not a steady stream at one speed. The device controls how much power the battery accepts, and it may lower the rate as the battery fills or heats up. A rate measured over a short interval can also jump when the displayed charge level updates in steps.

It is slower near 80 or 100 percent

Many devices reduce charging speed as the battery approaches full. Some pause or hold the charge near a chosen limit to reduce battery wear. Compare chargers at similar starting levels, rather than comparing a test that began at 30 percent with one that began at 85 percent.

The result changes when you use the device

The charger supplies power to the whole device, not just the battery. A bright screen, video call, game, or background update can use some of that power. The battery may then charge more slowly, or its level may barely rise even though the charger is connected.

One cable or charger is consistently slower

That can be a real difference. Chargers and devices negotiate how much power to use, and a cable can limit the result if it does not support the needed charging standard or is damaged. The percent-per-minute figure is an estimate based on battery level, not a direct measurement of watts, so use repeated tests as a comparison rather than treating a small difference as proof.

The battery level does not change

A short test may not last long enough for the browser to report a new percentage. The device may also be using as much power as the charger supplies, or may be pausing charging because of temperature or a charge limit. Check the device's charging symbol and system battery status before concluding that the cable is broken.

How to get a steadier result

Start at a similar charge level. Repeat each comparison when the battery is in roughly the same range. Avoid comparing a low battery with one close to full.
Let the device cool down. If it feels hot, stop demanding tasks and leave it in a cool, dry place before testing. Do not put it in a refrigerator or freezer. Heat can make the device limit charging to protect the battery.
Reduce power use while testing. Close games, video, navigation, and large downloads. On Windows 11, check Settings › System › Power & battery. On macOS, check System Settings › Battery. Power-saving settings can reduce background activity, but the screen and apps you leave running still affect the comparison.
Check for a charge limit or optimized charging. Some devices delay charging or stop at a set percentage. On an iPhone, look under Settings › Battery for charging options. Android labels vary by manufacturer, but check Settings › Battery. On a Mac, look under System Settings › Battery. If you change a limit for a comparison, restore the setting afterward.
Inspect the plug and cable. Disconnect both ends and check for dirt, looseness, fraying, or bent contacts. Try another suitable outlet and reconnect firmly. Do not use a cable with exposed wires or a damaged connector.
Swap one accessory at a time. Try a known-good cable with the same charger, then a known-good charger with the same cable. Use accessories that support your device's charging requirements. This helps separate a cable issue from a charger or device issue.

When the charger, cable, or battery may be faulty

Suspect the cable or charger if charging repeatedly stops when the connector moves, the device reports that it is not charging, or the same accessory is much slower across several controlled tests. If another compatible cable fixes the problem, replace the faulty cable. If another charger fixes it, replace the charger with a suitable model.

If multiple known-good chargers and cables produce the same problem, or the device gets unusually hot, swells, or shuts down while charging, stop using it and seek service. A swollen battery is a safety issue, not a reason to keep testing. Contact the manufacturer or a repair professional, especially if the device is under warranty.

Why percent per minute is not watts

A percentage describes a share of that particular battery's capacity. One percent on a large laptop battery represents a different amount of energy than one percent on a phone. Battery age and its usable capacity also affect how much energy a percentage represents.

The browser test uses battery information reported by the device to compare changes in charge level over time. It cannot directly read the electrical power flowing through the charger, and browsers may report battery updates in rounded steps. Treat the result as a practical, device-specific comparison. For the clearest answer, repeat the test under similar conditions and look for a consistent difference, not a single number.