The 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: 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.

Schematic design DEV-10711

Datasheet MAX17043

Datasheet MCP73831T

Datasheet TPS61200