I also found the phone powerbanks like the one you linked. These do output 5V but I don't like the fact that I can't see what it's inside the pretty box. Could be a 6/7V battery that gets its 5V output with a noisy regulator. I just want a normal 5V rechargeable battery :)
In the mean time 3 eneloops in series do their job just fine:)
1A is more than enough. Computer USB ports output 0.5A normally.
Good point; BTW I'm discussing this same thing on another forum and this link was posted: http://www.circuitsathome.com/adum4160-usb-isolator-assembly-guide
I'll try that circuit isolator first; if it proves noisy I'll go with the Eneloops.