Based on my experience with the 300, 600, and 900, if you were charging via the USB cable and your PC then you couldn't read at the same time because the Reader acted like a computer drive. If you were charging via the AC charger then you could read, but the reader was not acting like a drive in that circumstance.

I bought a two headed USB cable that had a standard USB connector on one end and a Y on the other with your choice of barrel charger connector or the micro-USB connector. If I plugged the standard connector into the PC and the barrel connector into the Reader it would allow me to read while charging.