The Efest Slim K2 is a professional portable two-slow Li-ion battery charger with a Micro USB charging port. It has a fast charging mode that is 1.0A (4.2V 2pcs x 1.0A) and can accept 3.6V or 3.7V lithium batteries in various sizes (sold separately). The Efest Slim K2 features reverse polarity protection, activation function, auto-detect charging function, over-charging protection, and short circuit protections. The spring in the charger is made by piano wire that provides a smooth sliding action when installing and removing batteries and steel cathode with low resistance and hard chromium plating processing is used to achieve a more precise charging voltage. Each slot on the Efest Slim K2 Charger monitors batteries separately and has a convenient LED indicator that displays battery life.