I could never find any lead that would charge and read a flash drive as well on my SGSII or SGSII and the same upto now could be said for my SGS4. I use my phone's camera a hell of a lot taking site photos at work what I love is to keep a USB drive plugged in permanently, send site photos to a previous configured folder and still use the vehicle charger on it. At the moment it is charged while I use Sygic to navigate, unplug, plug in USB drive, take photos, move them across to USB drive, unplug and plug in charger again. This can't be doing my micro USB port much good.
Samsung Galaxy Note 3 SM-N9005
ROOTED STOCK FIRMWARE PHILZ TOUCH RECOVERY
"The only foolish question is the question not asked"-Anon