The Golisi O4 Smart Battery Charger is simple. and has no buttons to play with is a portable four-battery charger. It charges almost any cylindrically shaped battery from 32mm to 70mm. With Dynamic Current Distribution Technology the Golisi O4 is able to properly charge your battery. The 2A slot offers lighting fast charging. Smart polarity gives you peace of mind when putting your batteries to charge. If placed in wrong nothing will happen. Golisi O4 is made with fireproof ABS+PC material and the springs and contact plates are military grade stainless steel. With its built-in USB port you can hook the O4 charger up to your portable device and when charged batteries are in it, you can use the Golisi O4 as a Power Bank!