Snap crackle and pop!

No, this isn't an advert for breakfast cereal, this is a post about my battery packs. A few days ago, after a "sick" rc drift session at the local multi-storey I went home and put the car away for the night. Next day I get my battery packs out and put them on charge, a few hours later as one of the Batteries lit up green to show it was charged I walked over to sap the battery for a flat one and noticed it was making a hissing and popping sound. Now, the Internet says this is natural and fine but I was abit suspicious of this so I took the battery out side and left it for a few hours. I went back to it later that night and checked for leaks or cracks and all was fine. I plugged it into the car and it worked fine! Confused much! I have no idea what happened but I'm going to keep an eye on that pack and check run times to see what affect this has had on performance. 

Peace!