Originally Posted by davidcampbell
The DC pack will only feed what the unit draws, and I doubt very much that it draws the entire 2000mA.
I have rigged up a USB charging cable for myself, USB pumps out 5v at 500mA max per port (I'm only using 1) and it charges a little slower than from the wall, depending on which computer I'm charging from, but apart from that it works great still and I can use the same cable to charge from other USB-charging devices like the one I have in my car.
The 500mA output will just mean it charges slower, and seeing how it's only a battery extender (IE, the oem battery is still required) and not a charging solution (the S7 can run without the battery off only the charge from the wall), the charge provided will be fine for extending the battery life.
500mAh as supplied by standard USB will charge but as you say only slowly.
It will not start a charge if the battery has been allowed to drop too low. That's common with all Lion batteries and is why you get a high current wall charger to do the job.
If you are using the device at the same time (and depending on the functions in use and the state of charge of the battery) you will definately struggle with any positive charge and will experience heat build up in the USB port, cable and device so be carefull!
If you are also using the device as a phone and get a call there will be an extra high peak current draw that has to be contended with and that complicates things further.
With all the tests that I have done allong these lines 1000mAh is a bare minimum to cope with eventualities and even then it's borderline.
I have blown car adapter fuses and had low current phone chargers get really hot.
I now only use 2000mAH rated chargers.