Defective first battery after 6 months

I had bought the battery from Pantona in December 2012. Unfortunately this does not work anymore since May-2013.
My Nikon D5100 returned the following error: "This battery can not be used, use a suitable battery for this camera.". After this period it is no longer possible to send the item back, which I think is very unfortunate because it is being touted as 100% compatible!

I have now ordered the originals battery from Amazon, because it only costs 38.

Update:

After I contacted the manufacturer to give me a new battery was sent as a bargaining chip. This works perfectly (until now). I now put my rating of 1 to 3 stars, as the exchange but still worked. Perhaps the battery was a special case.