So if my Phantom crashes due to a issue covered under warranty and you can't send back your battery if it's swollen or punctured during the crash.. How do they replace your battery..

They don't.......

DJI's Autumn (she is a regular here on the forum and works for DJI) stated one day that the batteries were warrantied for only 90 days. Someone else found something published by DJI that said the batteries were warrantied for 180 days. I can't find that source at the moment - maybe in the manual?

It would seem logical that if it could be proven your crash was warranty related that the battery could be replaced as well. However, I don't work for DJI - not sure what they consider logical!