Boho Tronics &reg; Spare Rechargeable Lithium-ion Replacement Li-ion Extended Battery 3800 mAh W/ Back Case - Compatible With Samsung Galaxy SII S2 S II Skyrocket i727 Advanced lithium-ion technology keeps phone working at optimum performance Extended battery capacity rated at 3800 mAh Use as a replacement or secondary battery Easy to install into phone Rechargeable and fits easily into your phone