You can use 5V/2A USB power source to power the device. Meanwhile you can use AA batteries as backup.
Please note when you have just connected the micro-usb power to the device, the green light will start flashing as the device will be running the USB connection mode for the first 15 minutes, but your device should sense and sync normally. It will quit this mode automatically after 15 minutes. Please wait about 30-45 minutes for the device to leave the USB connection mode and equilibrate with its environment to have the best temperature accuracy.