Is there anything an Arduino can't do? Well, for one, most of them can't be powered directly from a 3.7V LiPo battery; much less charge and monitor that battery. The SparkFun LiPower Shield takes care of this by combining the functionality of two of our favorite battery power boards: the Power Cell and the Fuel Gauge.
The LiPower Shield allows you to connect a 3.7V single cell Lithium polymer battery which it will boost up to 5V and connect to the Arduino board's 5V pin. The on-board MAX17043G+U IC is connected to the I2C lines (A4 and A5) so that your project can monitor it's own power supply. The configurable alert interrupt pin on the MAX17043G+U IC is broken out to D3 which will activate when the LiPo gets to 32% or lower.
The charging circuit is configured to charge the LiPo at 100mA but by adding a resistor to the supplied through-holes you can boost this to 500mA. There is a mini-USB port on the shield which allows you to charge the battery from a USB power source or you can supply a separate regulated 5V source on the "charge" header.
Note: We've decided to leave the power indicator LED (LED1) and its current limiting resistor (R3) off this board, as they were producing a significant drain on the battery. Please be aware that your board will have a few, shiny, unpopulated pads.
Note: There is a known hardware bug that will allow the LiPo to discharge below the point where the charging circuit will revive it. Thanks to the on-board fuel gauge, however, some clever programming could keep your project from draining the battery as it gets too low.
More information at SparkFun
This product has been discontinued at SparkFun.