The Golisi O2 Smart Battery Charger is super simple. There are no buttons to play with is a mini portable two-battery charger. It charges almost any cylindrically shaped battery from 32mm to 70mm. It is able to determine what type of battery has been placed in its docks and charge it according to that particular battery’s needs. The 2A slot offers lighting fast charging for when you need a battery charged in a hurry. Smart polarity prevention is a thing with the O2 charger. The body of the Golisi O2 is made with fireproof ABS+PC material and the springs and contact plates are military grade stainless steel and should last 100k cycles. Keep your batteries charged safely with the Golisi’s O2 Smart Battery Charger! AND with its built-in USB port, when your batteries are charged, you can hook the O2 charger up to your portable device and use the O2 as a Power Bank!!!