I get a lot of powerbanks to review, and they are generally all do exactly what they advertise, so I like to keep these reviews as short as possible.
Recently I was sent the Askborg ChargeCube 20800mAH powerbank external battery. This is the largest powerbank that I have been sent before, and its physical dimensions represent this. It is certainly not pocket-friendly, or light. But, you wouldn’t buy a battery pack like this to be pocket-friendly, it's more for heavy use on trips that you carry around in a bag. Perfect for a blogger on their phone and tablet all day.
Physically it is only slightly longer than my Nexus 6P, which been slightly smaller in width, however, I would guess it is over twice as thick as the phone and at least double the weight too.
The rest of it is pretty standard. There are 2 ports for charging, both are rated at 2.1A. It has a proper LCD to display the percentage remaining and it is charged via MicroUSB.
As you would expect this can charge your phone multiple times before dying. I used it on a trip for 2 days and it managed to keep my phone alive during heavy use without ever needed to rely on mains.
Overall, this is a good pack for long trips where you won’t be near a power socket any time soon. For general daily use, something smaller would probably be advisable.