I found a merchant selling an adapter
cable for usb charging of inteligent devices. They have what I consider a reasonable explanation of why a normal usb charger won't work. I haven't tried this adapter, so I can't vouch for it, but it sounds like it might work.
I'd like to know. I have at least six old Motorola RAZR mini-usb chargers that might work with it, but won't charge the reader as is.