I think it is powered with 5V when plugged in. The red light, which means "battery charging", never lights on when it is constantly plugged. However, if I unplug and replug it instantly, it lights on. The fact that it never charges suggests that it runs directly via USB power.if you power the SK01 with a USB charger, Will SK01 be supplied with 5Vdc ? or does the USB charger would only charge the battery and then the unit runs with 3.7-4.2 volts ?