USB powered with a charging current of 750mA. Compatible with lithium batteries with a rated voltage between 3.6V and 3.7V. NiMH batteries. Charging for dummies. There is no need for matching the polarities, as the charger can automatically recognize them when in use. All sizes compatible. It works perfectly on cylinder shaped batteries of variable diameters and lengths. Tangle-free flat cable design. Easy for storing and organizing.