Everything has a warranty on it. You should have posted where you lived, obviously, but for example in the UK anything you buy, including an Apple battery, must be free of defects and fit for purpose. And batteries are _never_ supposed to swell. They are supposed to lose capacity and stop working when they get old, but not to swell. Of course an old battery will eventually be out of warranty, and there is wear and tear (if you have one year warranty, but the battery is rated for 300 charges and you use them in four months, it won't get replaced), but saying that there is "no warranty on swelling" is nonsense.
I bought a cheap replacement battery for my old MacBook, which looked identical to the Apple one that it replaced, including all the tiny writing on the battery, but I had the impression that it didn't last as long.