It sounds like you either have a dud battery or the connection is loose. I would start by disconnecting the battery and cleaning all of the connections before you try anything else. As far as seeing if it is a dud, you could use a multimeter to see if the battery will hold a charge at all. Batteries off of eBay are a little hit or miss generally. If you used PayPal when you purchased it on eBay, its pretty easy to get your money back even if the seller won’t work with you.