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Posted by Bryan Liu

Have you ever plugged in the power bank for more than 24 hours and it still didn’t get a full charge? Plus, when using it to juice up your phone, you have to wait another 12 hours or even longer.

Indeed, generally the larger the volume is, the more charger you will get from the power bank. But you should never ignore the input and output rate, which directly affect the charging time. There is a formula for you to count charging time:

Rated Charging Time = Power Bank Capacity/ (input &output capacity* 85%)

Most power banks at present are designed with 5V 2A input standard, which stands for the biggest amount of flow it can accept. However, considering an estimated 15% power consumption during charging/discharging process, the actual input current would be 1700 mA (1.7A). Thereby, the charging time can be counted by this way:

Rated Charging Time = 20100 mAh / 1700 mAh = 11.82 hours

And if you are using a 1A rated charger, the charging time will be:

20100mAh/850mAh = 23.64 hours

So, it is not always the bigger the volume, the better the power bank. If it takes you more than 24 hours to full charge your phone, you would go crazy. Considering the above all analysis, you may get some idea about how to choose a good power bank. For your convenience, we’ll list some recommendations.

Zendure A6 20,100mAh Portable Charger

Zendure A6 is respectable product for its high efficiency, high capacity and good compatibility. It provides USB-C maximum output and input at 45W, which ensures impressive effectiveness.

Also, it is accompanied with regular 2.4A (Max) Micro-USB input and 2.4A (Max) USB-A output, making more devices compatible with it. Generally speaking, it can fully charge your MacBook 1.5 times, iPhone X 5.5 times and Galaxy S8 4 times. As for after-service warranty, Zendure promises a 45-Day Money Back Guarantee and 24-Month Product Replacement Warranty Card, which makes it both reliable and trustworthy.

Zendure A8 26,800 mAh

Designed with QC 3.0 technology, Zendure A8 is one of the fastest external batteries on the market for its capacity. There is one USB Quick Charge port and three USB 5v standard ports, which ensures your other devices will work while still charging your smartphone. Weighing 17 Oz, it is outstanding for portable use. You can easily fit it in your bag to take it on your travels. Its capacity is 26800 mAh, a satisfying volume that can easily extend your phone usage 7-9 times, and take only 10-12 hours to charge using a QC3.0 charger.

Zendure A5 16,750 mAh

Zendure A5 is a respectable product that is approved and used by a number of airlines such as Titan Airways for their pilots to charge iPads. Available in silver and black, Zendure A5 automatically detects your device and fine-tunes the output to charge it at maximum speed (up to 2.1A). All Zendure A series products can maintain up to 95% of its charge after six months without use, which means that you can put it away in your drawer for 6 months and when someday you are in a hurry to use a power bank, it is always ready to go.

Anker Powercore 20100

This excellent power bank has a long, narrow and slim design that makes it portable. 20100mAh is a grand battery capacity but the light weight (about 12 oz) of this mobile USB power bank makes it perfectly suited for handbags and backpacks. Besides, Anker recharges itself in 10 hours with a 2 amp charger, which is outstanding compared with normal phone chargers (generally 1 amp) that may take up to 20 hours. You may think 10 hours still seems a little time-consuming. Fortunately, its new version PowerCore 20000 Speed QC can get charged in about 4.5 hours using a Quick Charge 3.0 wall charger and charge your Quick Charge compatible smartphones to 80% in just 30 minutes.

In a word, there are mainly two factors that affects the charging time of a power bank, volume and input. Generally speaking, a larger capacity always accompanies with longer charging time. As for a 20100 mAh power bank, it takes about 11.82 hours under 2A input and 23.64 hours under 1A input. Just use the formula above to calculate whatever power bank you want!