Check charging rate near full before a festival

Your phone charges quickly at first, then seems to slow down as the battery fills. That is usually normal: charging control reduces the rate near full to protect the battery. You can compare the rate at different charge levels before relying on a charger or cable at a festival.

The Charger & Cable Test measures charging speed as a percentage of battery charge per minute. Treat it as a comparison, not a measurement of charger wattage or a guarantee of how long the battery will last.

Why charging slows near full

A battery does not take charge at one steady rate from empty to full. The device manages charging based on its charge level, temperature, battery condition, and the power available from the charger. It often reduces the rate as the battery approaches full, and the slowdown may be more noticeable at high charge levels.

Many phones also have a charging limit or battery protection feature that pauses or slows charging before the battery reaches 100%. This can be intentional. On an iPhone, look under Settings › Battery. On Android, look under Settings › Battery, though the exact options and names vary by device.

A percentage-per-minute reading is useful for comparing two setups on the same device. It is not a direct measure of electrical power. Battery percentages are rounded, and a percentage represents different amounts of stored energy on different devices.

Check the rate at different charge levels

1. Open the Charger & Cable Test on the device you plan to take. The test appears only on devices whose browser reports battery information.
2. Connect the charger and cable you expect to use. Keep the device in the same state for each comparison, ideally with the screen off and no demanding apps running.
3. Follow the on-screen instructions and note the displayed charging speed in percent per minute. Give the reading time to settle rather than judging it from a brief change.
4. Repeat the measurement at a lower charge level and again near full. Use the same charger, cable, outlet or power bank, and device conditions so the comparison is meaningful.
5. If you want to compare accessories, change only one item at a time. For example, keep the cable and device the same while testing a different charger.

The Battery Meter can also show charge level and charging state on supported devices. It is available only when the browser reports a battery, so it may not appear on every phone or browser.

Compare readings fairly

Compare similar charge levels

A charger may appear faster when the battery is low than when it is nearly full. That difference alone does not show that the charger has failed. Compare rates at roughly similar charge levels to judge whether a cable or charger changes performance.

Keep the device conditions similar

Screen use, navigation, gaming, video, and background tasks can use power while the device charges. Heat can also cause a device to limit charging. For a useful comparison, avoid using the phone during each reading and let a warm device cool in a shaded, ventilated place. Do not put it in a refrigerator or freezer.

Check whether a charge limit is active

If charging repeatedly pauses at a similar percentage, check the battery settings for a charge limit or optimized charging feature. A limit can make a near-full test look slow or stopped even when the charger is working as intended. Do not turn off a battery protection feature just to force a higher reading.

What the results mean

The rate falls near full

This is commonly expected. Charging management reduces the rate as the battery fills, and the exact point and amount of slowdown vary by device. A slower reading near full does not by itself mean the cable or charger is faulty.

The rate is lower with one cable or charger

If the difference repeats at a similar charge level and under similar conditions, that accessory may be limiting charging. Check that each connection is fully seated and that the cable or charger is intended for charging your device. A browser test cannot identify the accessory's exact power rating.

The rate changes while the device is warm or in use

Charging may slow while the phone is hot or doing demanding work. Stop intensive tasks, unplug it if it feels unusually hot, and let it cool naturally before testing again. If it repeatedly becomes very hot during ordinary charging, stop using that charger and cable and follow the device maker's safety guidance.

The reading is zero or keeps changing

Check whether the device reports that it is charging, whether a charge limit has paused it, and whether the cable is connected securely. Some browsers do not expose battery information, and percentage readings can update in steps rather than continuously. A missing or changing browser reading is not proof that the charger is defective.

Prepare for charging at the festival

Test the exact charger, cable, and power bank you plan to bring before leaving. Compare them while the phone is at a similar charge level, and check the rate again after changing only one accessory. A power bank's label or a brief browser reading cannot guarantee its remaining capacity, so start with it charged and carry a cable that fits securely.

Do not leave a phone or power bank in direct sun, under bedding, or in a tightly packed space while charging. If the device, charger, or cable is damaged, unusually hot, or smells burnt, stop using it rather than trying to confirm the fault with repeated tests.