Design: How huge  is the bank - is it going to be a pocket work or overload your backpack? Does it look great and feel well made (is there a guarantee?), or is it simply another plastic power bank? Is there a LCD that offers a correct readout of how much power stays (desirable over LEDs in high-limit banks)? Is it waterproof or rough, right for use at celebrations or when outdoors? Is there a built-in LED light or cord? Is there a solar panel for broadened use far from mains control?

Capacity: what number of occasions will this power bank charge your smart phone? Except if generally expressed by far most of power banks keep running at 65 percent proficiency, which implies a 3000mAh power bank won't completely charge a 3000mAh cell phone battery, however it might draw sufficiently near to get you out of a tight spot when you come up short on juice. The higher the limit the greater and heavier the power bank will be, however some more minimal outlines are accomplished by utilizing slimmer battery tech.

Input and Output: Not just the connectors themselves - Micro-USB, USB-C, Lightning and now even  AC adaptors - yet the quantity of those connectors (what number of gadgets do you have to charge without a moment's delay?).

Speed: If your smartphone underpins Quick Charge, search for a power bank that likewise supports the standard. When in doubt, 5W (5V, 1A) is moderate, 10W (5V, 2A) is quick, and anything higher than this is amazing.

Pass through charging: Remember that in the end, your power bank will run down, and when that happens you'll have to charge it and in addition, the gadget you were already using it to charge. The best power banks support pass through charging, which implies they can be charged in the same time as you charge any gadgets associated with their output, requiring just a single mains electrical plug and insignificant faffing around with connectors.
source: http://lisma.com.ng/2018/09/21/features-you-should-check-out-in-a-power-bank/