LiPower Shield (SparkFun Electronics)
SparkFun LiPower Shield Description: 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.