You should be able to use a power pack or external charging pack with all your mobile devices. As long as your power pack is providing enough power to trip the charging circuit, the amount the device will use is whatever the power pack has specified. You probably might want to do some research because some are made for smaller devices, and some can even charge a laptop.
I have a Ravpower 10000mah power bank
and it has been able to charge all my smaller devices with no issues. It has 2 ports, one port output is 5v1a and the other one is 5v2a. I have a iphone 4s, galaxy 3, kindle fire and kindle touch and it has been able to charge all with no issues.