I purchased a new Discovery unit about two years ago and a couple of months ago the battery would not charge. I purchased a new battery on line for $45 and still no charge. after much correspondence back and forth with IROBOT service support I was finally told that the unit could not be repaired and they offered to exchange for a replacement unit for $119 plus shipping, plus return of the defective unit (shipping at my expense). I would not purchase another unit and would not recomend this unit.iRobot Roomba 4220 Discovery SE Intelligent Floorvac Vacuuming Robot, Grey