Power bank can't keep up? What to test

Your phone or tablet is plugged into a power bank, but the battery percentage barely moves, or keeps falling while you use it. That does not always mean the power bank is faulty. A demanding app, a worn cable, a warm device, or a charging port with limited output can all make charging feel too slow.

Start by comparing the device's battery behavior with the power bank connected and disconnected. TooLab's Battery Meter shows charge level, charging state, estimated time left, and drain rate when your browser reports battery data. A second test can help compare the bank and cable with another charger.

Check whether the power bank is keeping up

1. Open the Battery Meter on the device you are charging. It appears only if the browser reports battery information for that device. If it is not available, use the device's own battery indicator instead.
2. With the power bank disconnected, note the charge percentage and drain rate. Use the device as you normally do for about 10 minutes, and note whether the percentage falls.
3. Connect the power bank using the cable you usually use. Keep the same apps, screen brightness, and wireless connections active for another 10 minutes. Check the charging state and whether the percentage rises, stays level, or falls.
4. Repeat the comparison with a known-good wall charger and, if available, a different cable. Keep the device at a similar starting charge level. Charging usually slows as the battery approaches full, so comparisons are fairest when the percentages are close.
5. For a closer comparison, open the Charger & Cable Test and compare the reported charge rate in percent per minute. Compare one setup at a time, using the same device and similar conditions.

Keep the test page open while you compare readings. A browser reading is an estimate based on the battery information the device provides. It is useful for comparing setups, but it does not measure the power bank's output in watts or prove the battery's health.

What the result means

The percentage rises with the bank connected

The bank is adding charge under those conditions. If it still feels slow, the device may be using power nearly as fast as it receives it. A bright screen, navigation, video, games, mobile data, or a video call can make a noticeable difference. Compare again with the screen off or with demanding apps closed.

The device says it is charging, but the percentage falls

The device detects a charging connection, but its current power use is greater than the charge it is storing. Try a less demanding task and check again. If the percentage rises when idle, the bank may be adequate for slower use but not for the workload you had running.

The percentage stays level with the bank

The power going in may be covering current use without adding much stored charge. Compare the setup with a wall charger, then try a different cable. A result that changes with a screen-off test points to device use as part of the problem.

The wall charger works better than the power bank

The bank, its output port, or its cable may be the limiting part. Check the bank's label or manual for the output supported by that port and compare it with the device's charging requirements. Some banks have ports with different capabilities, and connecting more than one device can reduce the power available to each.

Both chargers are slow

The device may be warm, close to full, or limiting its charging rate. It could also be the cable or the device's charging port. Let the device cool to room temperature, then compare again at a lower charge level with a different cable.

How to fix it

1. Close power-hungry apps. Stop navigation, games, video streaming, and video calls while charging. On an iPhone, check Settings › Battery to see which apps use the most power. On Android, open Settings › Battery; the exact battery usage menu varies by device.
2. Lower the screen load. Reduce brightness and turn the screen off when you do not need it. On Windows 11, open Settings › System › Power & battery and review power mode and battery settings. On a Mac, open System Settings › Battery and review available energy settings.
3. Try another cable and port. Use a cable known to charge another device reliably, and try a different output port on the bank. A cable that carries data or charges slowly may not be suitable for the power level you expect.
4. Check the bank's output rating. Read the label or manual and choose a port that supports the device. If you are charging a laptop, confirm that the bank supports the laptop's charging method and power needs. A USB-C connector by itself does not guarantee that a bank can charge every USB-C device at the same rate.
5. Let a warm device cool. Charging may slow when a phone or tablet gets hot, including in direct sun or inside a thick case. Move it to a cool, shaded place and avoid covering it while charging.
6. Charge one device at a time. If the bank is powering a phone and another device, disconnect the extra device and compare again. The available output may be shared between ports.

When the power bank or cable may be faulty

Test the bank with another device and a known-good cable, then test your device with a separate charger. If the bank repeatedly charges different devices very slowly or disconnects, while the separate charger works normally, the bank or its port may be failing. If changing the cable fixes the problem, replace the cable.

Stop using a power bank that is swollen, damaged, leaking, or unusually hot. Do not open it or try to repair its battery. Contact the seller or manufacturer about a warranty, or follow local guidance for battery recycling.

Why the comparison can change

Charge rate is not constant. Devices commonly reduce charging speed as the battery gets closer to full or when temperature rises. The device also controls how much power it accepts, so a higher-rated power bank does not force the device to charge faster. Use the Battery Meter and Charger & Cable Test to compare repeatable setups, not to treat a single percentage change as a precise measure of electrical power.

The Battery Meter works only when the browser can read battery information from the device, and nothing you record is uploaded because this test does not record audio or video.