Hyperion Samsung Galaxy SII 2x Battery + Travel Charger for Samsung Galaxy S 2 i9100 (NOT Compatible with Sprint Epic Touch 4G SII, AT&T i777 SII, or T-Mobile SII) NOT Compatible with Sprint Epic Touch 4G, ATT i777 SII, or T-Mobile Galaxy SII. Please see notes below with the item ASIN numbers for the Hyperion Batteries designed for the AT&T i777 Galaxy SII, Sprint Epic Touch 4G, and T-Mobile Galaxy SII. AT&T Galaxy SII: ASIN B005XOHQ6Y Sprint Epic Touch 4G Galaxy SII: ASIN B005X9GDMW T-Mobile Galaxy SII: ASIN B005ZSKN0E 2 x 1800mAh Battery and 1 x Universal Wall Dock Charger. Do not need to change back cover. The Smart LED shows charging status. Quick charge with automatic constant current control prevents battery from overcharging, short circuit, and electronic shock. The Smart LED shows charging status. Battery is designed specifically for Samsung Galaxy SII i9100, and will also work fully in the Samsung Galaxy SII i7777 ( US model from ATT ) BUT currently will not charge while in the phone and will need to be charged in the wall charger provided with the item currently.