Diy batterybank from 10-20 x 18650 or 26650

Hi

Edit, problem with edit sorry.

So Im trying to build a diy battery pack from either 18650 or 26650 batteries (getting them from a friend). Can I just use the following ebay case which is 5 dollars? I have a hobby charger which can calculate the capacity of a cell so if I get bad ones which are too differnet size than others, I will not use them.

Anyone know links to special high capacity 10x 18650 battery packs with multiple usb 5v outputs? (like hobby versions so you can diy).

These are 5 bucks on ebay. Can it be so easy?