What are the serial numbers? The first group of numbers on that little bar code label (ex B160812 ) is the model and manufacturing date, in this example August 2012. The second group is the actual serial number. Those units ship 18 to a box, so if the sn's of all of them that you had that were bad are all built at the same time and their numbers are +/- 20 or so (assuming you get them all from the same place eg distributor) then yes, there might be a bad batch.