So I can use power bank (Romoss 20000mAh) to charge a battery directly connecting it to Spark, but when I connect it to the Multiple charger unit (that came with fly more combo) it won't work.

Basically while I am using one battery J want to charge the other.

What can / should I do?

The USB port on the Spark battery charging hub from the Fly More Combo is not for charging. It's only for updating the firmware on the charging hub (there is no update yet). The supplied power adapter "brick" is the only way to use the charging hub. You can connect your power bank directly to your Spark, though.

Thats right.

you could get a powerbank with a powerplug-connection for charging the batteries using the wallcharger from the fly more combo.
I just ordered this one: http://amzn.to/2BD92hs

Hi, sir. Please follow the advice in 2# and I would recommend you use the QC 3.0 charger to charge your spark. Thanks for your support.