New laptop battery issues

I have a HP g71 that I just bought a new ebay battery for. I did like always and the sellers directions. Plugged it in and let it charge overnight. the next day I turned it on. booted right up like usual but the battery icon shows 0% charge. But it will stay running for almost 8 hrs (if left alone) 4 if I use it. But if while im using it and shut if off, it wont come back on like the battery is dead. don't matter if I just turned it on or use it 10-30 or an hour. just acts like I have a dead battery. do I need to return it or am I missing something?