The board can operate on an external supply of 6 to 20 volts. Leads from a battery can be inserted in the Gnd and Vin pin headers of the POWER connector. The adapter can be connected by plugging a 2.1mm center-positive plug into the board's power jack. The power source is selected automatically.External (non-USB) power can come either from an AC-to-DC adapter (wall-wart) or battery. The Arduino UNO WiFi can be powered via the USB connection or with an external power supply. (Or the device can act as an access point.) One useful feature of UNO WiFi is support for OTA (over-the-air) programming, either for transfer of Arduino sketches or Wi-Fi firmware. The ESP8266 Wi-Fi Module is a self contained SoC with integrated TCP/IP protocol stack that can give access to your Wi-Fi network. It contains everything needed to support the microcontroller simply connect it to a computer with a USB cable or power it with an AC-to-DC adapter or battery to get started. It has 14 digital input/output pins (of which 6 can be used as PWM outputs), 6 analog inputs, a 16 MHz ceramic resonator, a USB connection, a power jack, an ICSP header, and a reset button. The Arduino UNO WiFi is the same as a Arduino UNO Rev3 but with an integrated Wi-Fi module! The board is based on the ATmega328P with an ESP8266 Wi-Fi Module integrated (datasheet). This product is retired, check out the Arduino UNO WiFi Rev2