1900mAh Ultra Slim Rechargeable Lithium Polymer External Battery Skin Case for iPhone 4 4S Black Smart Battery (Optimized to lengthen your Phone performance time; No more out of power dilemma during Full Body Coverage for Phone 4G Lightweight, thin design, Non slip comfort grip Extended battery pack - 1900 mAh Four LED lights indicates the power level remaining the case (Each light represents 25% of remaining power)