@dta
1. They are in parallel. Therefore, even if they have different capacities, they will behave as a sum of both capacities.
2. No independent charging. That means do not put 2x cells with more than 0,1V of difference when setting it up.
Thanks for the additional explanation, but I still have some questions…
Assuming 2 batteries (in the above parallel-type powerbank) have different capacities but same voltage, then it’s safe to use in the powerbank, is that what is meant?
But if 2 batteries have a big voltage difference, then that’s a no-go, since (from what I understand), the higher voltage battery is going to “charge” the lower voltage battery at a possibly very fast charge rate. But what happens if this has been done? Will the batteries spark or explode? Or its just going to shorten battery life? Or do some other not-so-good thing (like damaging the powerbank circuitry)?
Of course you can avoid that by measuring battery voltage with a multimeter or battery charger. Nothing very wrong can happen anyway since the current flow will be limited by the sum of both cells internal resistances plus contact and spring resistances, and the initial current inrush soon tapers very much like the current tapering which happens upon entering CV phase during a standard charge. If you witness sparks or fumes out of the circuitry upon cell insertion you are either inserting a cell in reverse :facepalm: (DO NOT!) or cell voltages are too dissimilar. Better avoided but no big deal. 
:-)