Amazon does not actually refurbish anything (just minimal checks to see if it powers up) and then call it renewed, and if it is a third-party seller, as often as not, it is just a repackaged used phone. Last I checked Apple will also not replace a third-party battery - look up the warranty terms online. Personally, I would just return the device for a refund. At least pre-owned from Best Buy has actually been checked out. Amazon "refurbished" is no better than eBay but people think otherwise due to the name. You have no idea what other problems the device may have and you have already been scammed on the battery front. Don't perpetuate it (and help scammers stay in business) by keeping something that is anything but a deal.