[Plextalk] Charging the PTP1

Dearest PTP1 Users! Does anyone know how I can willingly use the USB cable to charge the PTP1? It only happens by accident on rare occasions when I am actually making an attempt to use the USB cable to connect the PTP1 to my computer. I then have to restart the machine in order to make it possible to connect to my computer instead, however there are times that I would like to charge the PTP1 with the USB cable. All help welcome! Thank you.