Efest LUC S2 Two Slot LCD Battery Charger. Efest LUC S2 is a high-tech smart LCD charger, which can show the charging status clearly when charging the 3.7v batteries. Designed with two built in independent charging channels, which means two 3.7v batteries can be charged at the same time with the Efest LUC S2. Made of good safe performance. The Efest is a high quality device with advanced battery charging numeration. It will protect batteries automatically during charging.