T-Mobile QCell MyTouch 4G Slide Beige 3800mAh Extended Battery + Extended Battery Cover (NOT Compatible with MyTouch 3G / MyTouch 4G) MyTouch 4G Slide 3800mAh Extended Battery. Highest Capacity Battery in the 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