I wouldn't even watch it. Once you notice it is now "different", time to retire it. It won't get better and can only get worse. I have no issues using 3rd party batteries but also I wouldn't risk using any battery once it has exhibited any amount of deformation.
Did you call them out on it? That is pretty inexcusable especially as I noted above an authorized service center was continuing to use an obviously defective battery in customer's equipment. You should have made a big stink with Panny to see if maybe you could have wrangled a free battery out of them or something.