Re: coin cell battery safety
Even then, I wouldn't be too worried. One of my "cautionary tales" happened early on my first job out of college at a tiny electronics manufacturer.
I was testing/repairing some real-time clock modules that had just been assembled and had removed the coin cells from the ones I couldn't fix. Not thinking, I put them all -- a few dozen -- into a big ziploc bag and placed it on the pickup table for restocking. Then about fifteen minutes later, our office manager picked up the bag and commented "Oh, this bag is nice and warm!" (it was rather cold outside).
My head snapped around when she said that because it had just hit me how stupid I was. Unfortunately, my boss was standing next to her as she said it and glanced down at the bag, then glared at me and stormed off into his office without saying a word.
So you're safe, just don't short the terminals together.