How to check if a power bank charges well
Compare a power bank with a known charger using your device's charge rate, and learn what slow charging or heat can tell you.
Your phone is plugged into a power bank, but the battery percentage seems to crawl upward, or not move at all. The power bank may be working normally, or the cable, phone settings, temperature, or charging standard may be limiting the speed.
Compare the power bank with a charger you know works, using the same device and cable. The Charger & Cable Test measures charging speed in percent per minute, so you can compare setups without guessing from the battery icon alone.
Compare the power bank with a known charger
- Open the Charger & Cable Test on the device you want to charge. It is available only when your browser reports battery information. If the tool is missing, your browser may not expose that data.
- Use the power bank when your device is between about 20% and 60% charge. Connect it with the cable you normally use, and wait a few minutes for the charging rate to settle.
- Note the displayed speed in percent per minute. Keep the device's screen and apps in the same state throughout the comparison. Avoid gaming, video calls, navigation, or other demanding tasks while testing.
- Repeat the test with a known-good wall charger, using the same cable and a similar starting battery level. If you want to check the cable too, compare with another compatible cable while keeping the power source the same.
Battery percentages do not increase at a perfectly steady rate. For a useful comparison, test the setups under similar conditions and look at the rate over a few minutes, not a brief change of one percentage point.
What the result means
The power bank charges at a similar rate to your usual charger
The power bank is probably doing its job for that device and cable. It may still charge more slowly than a wall charger, especially if its output is lower or it does not support the fast-charging standard your device uses. A lower rate is not automatically a fault if it meets your needs.
The power bank is much slower than the known-good charger
Something in this setup is limiting charging. The power bank may have a lower output, the cable may be damaged or unsuitable for fast charging, or the power bank and device may not share a faster charging standard. Repeat the comparison with another cable before deciding the power bank is the problem.
The battery percentage barely changes or goes down
The device is receiving little power compared with what it is using, or it may not be charging reliably. Close demanding apps, check the cable connection, and test again with the screen off if your device and browser allow the test to keep running. The result is a net battery change, not a direct measurement of the power bank's electrical output.
The rate slows near a full charge
This is normal. Phones and tablets usually reduce charging speed as the battery gets full, and some also slow charging when the battery is hot or cold. Do not compare one setup at 30% with another at 95% and treat the numbers as a fair test.
How to improve a slow charge
- Check the cable and connections. Unplug both ends and reconnect them firmly. Look for a bent connector, fraying, or dirt in the device's charging port. Try another cable that supports charging, not just data transfer.
- Use the right power bank port. Some power banks have several ports with different output limits. Check the markings on the bank or its manual, and try the port intended for faster device charging. A USB-C port does not guarantee that every device will charge at the same speed.
- Reduce power use during the test. Close games and video apps, pause downloads, and avoid using the device while measuring. If the phone is hot, remove a thick case and let it cool in a shaded, ventilated place before trying again.
- Check the device's charging settings. On Android, open Settings › Battery and look for charging or battery protection options; names vary by manufacturer. On iPhone, check Settings › Battery for charging information and battery options. Optimized charging may pause or slow charging in some situations, particularly near a full battery.
- Restart the device and retest. A temporary software problem or a busy background app can affect the battery reading. Restart, reconnect the power bank, and compare again at a similar charge level.
- Compare another device. If the power bank charges a second compatible device normally, the limit may be the first device's port, battery, settings, or charging compatibility. If both charge slowly with the same cable, test another cable or power source.
When the power bank may be faulty
Suspect the power bank if it charges multiple compatible devices slowly with more than one good cable, or if its output repeatedly cuts in and out. If it has a charge indicator, check whether the bank itself has enough charge. A nearly empty bank may not deliver the same result as a fully charged one.
Stop using a power bank that is swollen, leaking, smells unusual, or becomes dangerously hot. Do not open it or keep charging it to see what happens. Follow the manufacturer's safety and warranty instructions, and replace it if it is damaged.
Why the percentage is not a wattage reading
The test reports how quickly the device's battery percentage rises. It does not measure the power bank's output in watts, and two devices can gain different percentages from the same power source because they have different battery sizes and charging behavior. The percentage rate is most useful for comparing the same device, at a similar battery level, with one change at a time.
If your browser does not show battery information, try the test on another supported browser or device. Battery data depends on what the browser makes available, not just on whether the power bank is connected.
