I have yet to find a single battery on eBay that is an actually genuine Apple battery. Be very careful, I have seen way too many MBP/MB/MBAs over the years with fried SMC's or LB's because of eBay knockoff batteries. Your best bet honestly is to find a used battery on eBay, from a pull, with good health. It is either that, buying from Apple, or OWC
http://eshop.macsales.com/item/NewerTech/BAP13MBU65W/