Boho Tronics &reg; Spare Rechargeable Lithium-ion Replacement Li-ion Extended Battery 3600 mAh W/ Back Case - Compatible With T-Mobile Samsung Galaxy S 2 II Hercules T989 - Black Advanced lithium-ion technology keeps phone working at optimum performance Extended battery capacity rated at 3600mAh Use as a replacement or secondary battery Easy to install into phone Rechargeable and fits easily into your phone