Newbie query: Can I use the USB lead (for connecting to computer) to charge up X100T's battery from a portable power pack, say, if I'm out and about and need to top up the battery while having lunch ... I have a power pack with a '5V' output and 2 USB points with either '1A' or '2.4A' MAX (output?). I anticipate recharging to be slower than via a charger but don't mind that so long as it doesn't blow the mind of the X100T. (FYI: the power pack happily charges up an iPad Air.)