T-Mobile QCell MyTouch 4G 3600mAh Extended Battery, Extended Battery Cover- NOT Compatible with MyTouch 3G / MyTouch 4G SLIDE 3600mAh Extended Battery! Best Li-Ion Battery in Market! Designed in Canada! Double Your Battery Life with this High Capacity Battery! Comes with Free Battery Cover! DYNAStop overcharge IC stopper built in! Voltage: 3.7V / Premium Quality and Best Material used!