OK, essentially I'm looking to invest in a portable external battery pack, something like this one: http://tinyurl.com/brxpdhz (amazon.com).
However, I don't know how many amps (in a 5 volt current, since that's what most of these seem to use) is optimal for charging my smartphone (Samsung Galaxy S2 Epic Touch). Ideally the more amps the faster the phone will charge, but I know it isn't that simple.

To the extent of my knowledge about electricity, there are 3 essential factors in charging devices:
1. Output current (coming from battery)
2. Wire capacity (electricity able to be transferred)
3. Maximum draw current into device (max electricity phone will accept, and I do not know the draw current for my phone--I'm having trouble finding it online too)

The common battery packs I've been looking at usually have two USB output ports, usually either 1) one 1V output and one ~2V output OR 2) two 3V outputs. I'm not sure which one is optimal for charging my cell phone.

To the question: Is having a higher current, like 3V, going into a low-drawing (term I made-up) device, say 1V for simplicity's sake, bad (i.e. will battery be wasted)? Or is there no serious down-side (i.e. just that my phone won't charge faster)?


Any knowledge you can share with me is very much appreciated.

(also if you aren't sure about an answer but know a good hardware forum I could ask about this on, I would appreciate it if you give me a link)