Chris, the above comments are accurate & also the lids can be very slightly out of round, but that will also fix with cooking some more.......
Shouldn't really affect the heat retention very much at all......i.e.: whatever minimal heat you do lose, then the kettle temp settles there.....make sense?
As for charcoal, it's an absorbent.....a very, very good one............
When people suffer from acute alcohol poisoning (too much booze, too quickly), the hospital will give them, you guessed it: charcoal.....not heat beads, but a different form of it to soak up the toxicity.......
If your bag was open, a common effect will be: tough to light, right after a bout of rain.............
If the bag is open, consider some kind of closeable container.....I've used large plastic laundry soap buckets, cat litter buckets, either has a snap close lid & will help a lot with keeping moisture at bay.......the stuff is a moisture sponge.........
Helps just to get in the habit of closing up the bag by rolling the open top down tight, too!!!!