The 4HR-3UWX 4-AA rechargeable battery pack utilizes SANYO"s new, Double X (XX) battery Powered by eneloop which provides 2500mAh of performance for long lasting, high power capacity, extreme applications. XX batteries are the perfect choice for powering high current consuming devices such as photo strobe flash lights; providing more than twice the number of flashes per recharge in less than half the time as compared to conventional alkaline batteries!