I have charged a new battery (Zippy 4S1P 4200mAh 30C) and it seems to have bulged down one side, its more like an air pocket and is not solid. I hadn`t used it and it was balance charged correctly along with the others.
Unfortunately its out of warranty as I got it at the beginning of the year, I got 8 and the other seven are fine.

Would this be considered safe to use?