The Fio v3 is a new spin on the Arduino Fio hardware powered by the ATmega32U4.Not only is it small and LiPo-ready, it’s a very capable XBee-ready development board. The JST-connector and 3.3v system voltage make this a great development tool for portable devices, simply plug in a Li-Poly battery and you’re ready to go. Wireless sensor networks and communication are made easy by the on-board XBee socket.
The ATmega32U4, running at 8MHz, makes it possible for you to use the on-board USB jack not only to charge a connected Li-Poly battery but to actually program the device! Because this board uses a similar bootloader to the one on the Pro Micro, you will need to download and install the special software driver below. There’s also a board definition add-on for the Arduino IDE which will add support for this board.
Key Features

ATmega32U4 running at 8MHz

Arduino-Compatible Bootloader

XBee Socket

Lithium Polymer Battery Compatible

MCP73831T LiPo Charger

Reset button

On/Off Switch

Status/Charge/RSSI LEDs

Resources

Schematic

Eagle Files

Hookup Guide

Datasheet(MCP73831T)

Firmware Note

Board Definition Files

Arduino Addon Files

Arduino Addon Files (IDE 1.5+)

GitHub(Design Files)