How to compare charging speed at two wall outlets

Your phone or laptop seems to charge faster from one wall outlet than another. That can happen, but the outlet is only one possible cause. The charger, cable, battery level, and device temperature can all change the result.

Use the same device, charger, and cable at each outlet, then compare the charging rate under similar conditions. TooLab's Charger & Cable Test measures charge speed as percent per minute on devices whose browser reports battery information.

Compare the two outlets

Open the Charger & Cable Test on the device you want to check. Use a laptop, tablet, or phone that reports battery details to its browser.
Plug the same charger and cable directly into outlet A. Keep the device in a similar state for the whole test: close demanding apps, avoid using it, and keep it in the same room. Note the starting battery percentage and the displayed charging rate.
Let the device charge for about 10 to 15 minutes. Note the ending percentage and rate. The percentage change is useful if the displayed rate moves around during the test.
Move the unchanged charger and cable to outlet B. Start at a similar battery level, ideally within a few percentage points of the first run, and repeat for the same amount of time.
Repeat the comparison later, swapping which outlet you test first. A second comparison helps show whether a difference is consistent rather than caused by changing battery level or temperature.

Do not deliberately drain the battery just to match the starting level. Wait until the device naturally reaches a similar charge range. Try to compare below about 80 percent, because many devices reduce charging speed as the battery gets fuller.

What the result means

The rates are close

The outlets are delivering similar charging results with this setup. A small difference is normal. The displayed rate is a practical comparison, not a direct measurement of the electricity coming from the wall or the charger's output in watts.

One outlet is slower in a single run

That does not prove the outlet is faulty. The device may have warmed up, the battery may have started at a different level, or an app may have used more power during one test. Repeat the test with the same charger and cable before drawing a conclusion.

The same outlet is repeatedly slower

A repeatable difference is a reason to check the setup, but it still does not identify the outlet as the cause. The charger may not be seated firmly, an extension or power strip may be involved, or the device may be limiting charge speed. Test the outlets with another known-good charger and cable if you have them.

The test shows no battery details

Some browsers and devices do not report battery information, so the charging test may not be available. This is a browser limitation, not proof that the battery or charger is broken. Try the test in a supported browser on a laptop, tablet, or phone that reports battery data.

How to make the comparison fair

Keep the charging gear identical. Use the same charger and cable at both outlets. If you change either one, you are comparing the charger or cable as well as the outlets.
Match the battery level and test time. Charging speed often changes as the battery fills. Compare similar starting percentages and use the same test duration for each outlet.
Keep the device cool and idle. Heat can make a device reduce charging speed. Do not run games, video calls, or demanding downloads during one test but not the other.
Check for extra connections. If the charger is plugged into a power strip or extension, remove it from both comparisons only if you can reach the wall outlet safely. Do not use a damaged or loose extension cord.
Swap one part at a time. If the difference remains, test a different charger while keeping the cable and device the same. Then, if needed, test a different cable with the original charger. This helps separate an outlet issue from a charger or cable issue.

When the outlet may need attention

A charging-rate test cannot measure outlet voltage, wiring quality, or electrical safety. A normal wall outlet should not usually make the same charger charge much more slowly than another. A persistent difference can justify asking an electrician to inspect the outlet, especially if other appliances also behave oddly there.

Stop using an outlet if the plug fits loosely, the outlet or plug becomes unusually hot, you hear buzzing or crackling, or you see sparks, scorch marks, or a burning smell. Do not open the outlet or try to repair its wiring yourself. Have a qualified electrician inspect it.

Why charging speed changes during a test

The percent-per-minute figure is a rate based on the battery's reported charge level. It is not a laboratory measurement of power. Battery percentage is rounded, and the device may adjust how quickly it charges based on temperature, battery condition, and how full it is.

For that reason, treat a small difference as normal variation. A clear difference that appears again with the same device and charging gear is more useful, but the test alone cannot tell you whether the wall outlet, charger, cable, or device caused it.