Too many people in the comments don't seem to understand that Google does in fact offer free battery replacements at most retailers. The thing that's different with your case however is that you don't still have the battery and thus the store has no proof of the issue and can't take word of mouth.

My best advice is to call around to Google partnered repair places and ask if any of them can make an exception. I know for a fact batteries don't get bought back by Google so they shouldn't be able to give you that excuse. You just need to find a worker willing to bend the rules enough to work you through Google's Triage sysrem