4. Wide Compatibility

Technically, you should opt to buy a power bank that can actually charge your phone. For instance, I once got a power back that couldn’t charge my blackberry z10. The one I am currently using can charge any USB powered devices as well as the following phones. It also supports quick-charge. Intelligently detects and charges  iPhone 8 · 8 Plus · X · 7 · 7 Plus · 6 · 6 Plus · 6S · 6S Plus · 5, iPad 2 · 3 · 4 · Air · Air 2 · 2017 · Mini 2 · 3 · 4, Samsung Galaxy S8 · S8+ · S7 · S7 Edge · S6 · S6 Edge · S5 · S4 · Note, Google Nexus, Kindle Fire HD/HDX, LG, Fitbit, BT earphones and more. FOR IPHONE/IPAD: It’s normal that the blue indicator won’t light; rest assured that charging is at max speed allowed by Apple. USB PD not supported. Does not fast charge Pixel phones.

5. Battery material

It is very important to take care of safety, so buy a power bank with a lithium-polymer cell

6. How fast does it charge your device vs how long it takes the power bank to be fully charged 

Not all premium power bank out there supports the adaptive quick charge. See my list above for names of makers that produce power banks with quick charge solution. Charging speed is how fast the power bank can charge your device. If you have one that supports fast charging, and your phone has fast charging capability the said power bank will charge your 3000mAH fully within 1 hour. As for charging time, I mean how long it takes for your power bank to be fully charged.

As for me, if I use an ordinary adapter, it will take me 6 hours. However, if I use an iPad original adapter, it will take me 5 hours. By contrast, if I use my fast charging adapter, the power bank will be fully charged within 4 hours. You can get this information from the product features or specifications. Moreover, you can contact the seller for such information.

7. Charging methods

I was so happy when I received my power bank and I realized I can change it through three methods. To charge the ZMI portable power bank, you can use a USB cable that you connect to any USB port like your PC, home theatre and son. Secondly, you can charge it using a USB-C cable and finally, you can charge it with your normal micro USB cable. Please watch out for these as it might influence your decision. As of now, you can charge power banks in the following ways:: Solar power(sun), USB charging,  USB c, usb-a. Most power bank can only charge when connected to a micro USB Cable that is connected to a wall outlet. If you cherish some extra, then go for one that offers multiple charging methods

7. Portability

One of the main reasons to buy a power bank is the portability factor. The ability to charge your devices while on the move because you can simply take a charger with you, is a huge plus. Be careful with the inexpensive ones with big capacity. Many times you get what you pay for, meaning they may not charge your gadgets properly, or even worse, break down on you.

Power banks buying guides: Miscellaneous considerations

• If you own two phones, then you can buy a power bank with two charging ports.
• Also, make sure you buy a Power Bank with LED indicator so that you can know how the battery status of your power bank
• Current is another factor which determines charging time. If the current rating of the power source is lower than the battery, then the battery will take a long time to charge.