Actually, I have a question about the batteries with passthru if someone knows ... does the battery supply the power to the attachment, and the charging occurs in the background when the battery is idle, or is the draw direct from the usb plug? If its the battery that is actually powering the attachment, then the background charging I assume would draw less than the 500ma USB 2.0 standard and could be plugged into a computer safely ... if that is indeed how it works.
I'm not sure if all passthru batteries work alike, but I CAN say that with my eGo passthru battery I vape from the battery when it's plugged in, not from the USB connection. If I use it after it's fully charged but still plugged in, the charging light will light up, indicating that power was drawn from the battery itself. So for the model that I have it's only the battery that powers the PV. The USB cable only charges the battery.