The Portal Cord is much different than basic powerbanks. It is more of a replacement for your everyday charging cable rather than a replacement for powerbanks.
External batteries require you to bring along a separate cord for your device, on top of that they require an additional cord to charge the external battery. This becomes a burden of bringing along additional cords, and if you forget to charge your external battery it becomes worthless.
The Portal Cord does all of the charging for you, and gives you the most efficient boost, and ease of mind knowing there's always extra power in your cord.
We have been looking into adding more mAh into the Portal Cord, but unfortunately it would alter the design making it much bulkier. Also the design and development would be brought back to square one, and delay the estimated shipping date.