I had a similar concern back in early January. I received a new laptop battery pack while visiting a relative over the holidays. I decided to harvest the cells from the bad pack, so that it would be easier to take back home. I wrapped them in individually in plastic, and seated in a plastic bag. Put in carry-on. No problems at all. Not even a TSA delay. I would avoid putting the batteries in checked luggage. Someone here mentioned that it could be under greater scrutiny since bags in cargo hold cannot be accessed in flight (e.g. fire).