One Windows is simply not enough! Call US +1 877 734 6106 to find out Call UK 0800 027 2002 to find out HyerDrive4 6 hour backup battery   Specification Features: 7.4V 4800mAh Li-Ion rechargeable battery made of 4 high quality LG cylindrical 18650 cells Dimension: 2.8"L x 1.4"W x 1.4"H ( refer to picture ) Weight: 0.3 Kg Max. charge current: 1.0 C (2.4 A) Max. discharge current: 2 C ( 9.6 A) Cut off voltage: 5.2 V No memory effect and longer storage life than NiMH battery Totally environment friendly, 100% recyclable Light-weight, and higher energy density than any rechargeable battery. Installed IC chip prevents battery pack over charge and over discharge, helps protect battery chemistry integrity and prolongs battery life.