You may need this item if you want to power your Arduino with a 3.7V LiPo battery to make it become a portable device. It made up of a “power cell” and “fuel gauge”, it 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 D2 which will activate when the LiPo gets to 32% or lower. The charging circuit is configured to charge the LiPo at 500mA and there is a mini-USB port on the shield which allows you to charge the battery from a USB power source.