The Charley is considered class III at low to medium flows and IV at high flows. High water up to June and low water after. There are no gauging stations, so all flow measurements are just guesses. It is believed that high flow is in the 2000 to 4000cfs range. It is called the most beautiful river in Alaska. Air access only. 6-10 days to float and you can hike to a crashed B-24 at the put in! Early June trip will give you the high water and before the mosquito population peaks. 6 days is non stop, 10 days if you allow rest and hike days. You get 36 more river miles if you do it during high flow. Summer time the water warms up quite a bit, but you will have drag, push or pull the boats through the high water class IV stretch. It is a much better run at high water. Either way, it is not cheap to fly in and you will want plenty of bug spray and head nets.
If you are ever up this way, I have Andrews book and it is well worth getting a copy if you can.