[Sean "Puffy" Coals]

***Disclaimer: I am NO expert***

In my experience, air leaks cause temps to be too high, not low.

Low temps indicate a draw/intake problem- not enough oxygen to feed the fire. I'm not familiar with CharGrillers, but maybe check to make sure nothing is interfering with your intakes or exhaust. Ash build-up MAY be the issue if your temps are ok at the start of the cook (less ash in the pan) but drop off later as the ash builds up.

I've never heard of charcoal going bad unless the bag got totally soaked thru and coals got wet directly. Humidity is pretty much kept out by the paper bags the coals come in. Condensation is a different story, but there would be other evidence if that was the case, ie. moldy or crumbly/moist briquettes.

Plus, as the cook goes on, any humidity/moisture should evaporate out from the heat of the fire as time goes on. This would make your temps get higher as time goes on but probably not by much if at all.

That's my .02, hope it helps. I'm sure others will have more info for ya. Hope you get it figured out.