... out of power,it can be just attached perfect Attachable Battery Pack for iPhone and iPodFeatures: 1,Made for iphone4,3G ... ,Non-slip grip design Product Modle:T4 Color :white Battery:Lithium-polymer battery Capacity:1500MAH(3.7V) USB Output voltage:5V USB ... . Silica gel material, special shape design. Charging Anti-skid designThere is a micro USB port in the side, used for data transmission ...