I'm no pro, but definetely not a good thing. I know that for sure. I would probably be too worried to use it, so I'd strongly suggest replacing it and taking better care of the next one. Also, on top of what the other person who replied said, make sure you are storing them at the proper voltage if you have to store them for over a week I'd say. Temperature also plays a big role, I know some people who have dedicated fridge space for lipos. (A little weird if you ask me) good luck to you though.