I bought one of eBay a few weeks back too and I think it's a fake, because it says (claims) it's Lithium Ion and I can't find any BST-41's that are anything but Li-Po. With that said however, the hologram is nearly identical to the original and the performance/life of it is MUCH better than my original one - which I know is worn out, but still.
I can't find any site where to get this one. I assume the eBay seller was reselling something from China, but I can't get in contact with him either. I found something on alibaba
(which is wholesale though, I know) that claims to have Li-Ion BST-41's but there is no photo of the front of the battery. Anyway, I have attached photo's. Sorry about the moderate blurriness, I ain't good on a camera. If anyone can find this same type of "genuine" Li-Ion BST-41, I recommend it. I think I paid $28 (AU) for it (free postage).
EDIT: The alibaba one is not the same as mine, markings on the back are different.
EDIT2: I remember the original listing might have been from Amazon because I couldn't find the battery in my eBay history, but I can't find anything on any of the sites I buy goods from. I do remember though that it came in retail packaging (orange and white I think? Or is it green and white?) And the product listing said it was for X1. But I run an X10, same BST-41 (also same as Xperia Play).