If you have ever used a power bank to charge your phone or other devices, you may have noticed that sometimes it gets stuck at 99% and does not reach 100% even after hours of charging.
This can be frustrating and confusing, especially if you want to use your power bank to its full capacity. So, why does this happen and how can you fix it?
Why Power Bank Stuck At 99%?
The main reason why your power bank gets stuck at 99% is because of the way it measures its battery level.
Most power banks use a simple circuit called a voltage divider to estimate how much charge is left in the battery. A voltage divider consists of two resistors connected in series, and it produces an output voltage that is proportional to the input voltage.
The output voltage is then fed to a microcontroller, which converts it into a percentage and displays it on the LED screen or indicator lights.
However, this method is not very accurate, because the voltage of a battery does not decrease linearly as it discharges.
Instead, it follows a discharge curve that depends on the type and quality of the battery, the temperature, the load, and other factors.
For example, a typical lithium-ion battery has a nominal voltage of 3.7V, but it can range from 4.2V when fully charged to 2.7V when fully discharged.
As you can see from the graph below, the voltage drops rapidly at first, then slows down, and finally drops again near the end of the cycle.
![Discharge curve of a lithium-ion battery]
This means that when your power bank is almost full, the voltage divider may not be able to detect the small changes in the battery voltage, and it may report that it is still at 99% even though it is actually closer to 100%.
This is especially true if your power bank has a high capacity, such as 10,000mAh or more because it will have more cells in parallel that will increase the total voltage.
How to Power Bank Stuck At 99% Issue?
There are a few ways you can try to solve the 99% problem and make your power bank reach 100%. Here are some of them:
#1. Use a different charger or cable
Sometimes, the problem may be caused by a faulty or incompatible charger or cable that does not deliver enough current to your power bank.
Try using a different charger or cable that has a higher output rating and see if that helps.
#2. Reset your power bank
Some power banks have a reset button or switch that you can press to reset the circuit and recalibrate the battery level.
Check your power bank manual or look for a small hole or button on the side or bottom of your device and see if you can find it. If you do, press it for a few seconds and then recharge your power bank.
#3. Drain and recharge your power bank
Another way to recalibrate your power bank is to drain it completely and then recharge it fully.
This will help reset the discharge curve and make it more accurate. However, you should not do this too often, as it may shorten the lifespan of your battery.
#4. Replace your power bank
If none of the above methods work, then your power bank may be defective or damaged and you may need to replace it with a new one.
Look for a power bank that has a more advanced circuit that can measure the battery level more accurately, such as one that uses a coulomb counter instead of a voltage divider.
A coulomb counter measures the actual amount of charge that goes in and out of the battery, rather than relying on the voltage.
Conclusion
A power bank stuck at 99% is not uncommon and does not necessarily mean that your device is broken or faulty.
It is usually caused by an inaccurate measurement of the battery level by a simple circuit called a voltage divider. You can try some of the methods mentioned above to fix this problem and make your power bank reach 100%.
However, if nothing works, you may need to replace your power bank with a better one that has a more accurate circuit.
