What you have is probably a counterfeit, or fake, battery. A real Motorola battery has a chip inside that controls charge/discharge and allows the phone to identify it as being a real OEM (original equipment manufacturer) battery. Most batteries sourced in China and sold on eBay are not OEM batteries, they are fakes. They may look the same on the outside, but they are not the same on the inside. If the phone can't validate the battery it will either display a warning, or not charge at all, depending on the phone.
There is a good reason for this. To save cost, counterfeit builders often buy rejected lots of cells, and/or leave out safety components. A few years back there was a rash of phone and digital camera fires traced to defective batteries, and they turned out to be fakes. This led to the new generation of "smart" batteries.
There is nothing to do except try to get a refund from the eBay seller and then get a real Motorola OEM battery from a more reputable seller. I also suggest you complain directly to eBay. They have a "Buyer Protection" policy and you might be able to get your money back.