Description of USB LiPoly Charger Single Cell The SparkFun USB LiPo Charger is a basic charging circuit that allows you to charge 3.7V LiPo cells at a rate of 500mA or 100mA. It is designed to charge single-cell Li-Ion or Li-Polymer batteries. The board incorporates a charging circuit, status LED, selectable solder jumper for 500mA or 100mA charging current, external LED footprint, USB input, two pre-installed JST connectors for SYS OUT and BATT IN, and (back by popular demand) a barrel jack connector. There is also a ‘SYS OUT’ with a pre-installed JST connector which allows you to connect the charging circuit directly to your project so you don’t need to disconnect the charger each time you want to use it. Click here to know more about this product.