Irwin can't digest his food unless he can get heated up to around 80 degrees, which is why he wasn't eating. During the winter, Charlie will eat when it is cold because he can come back to his heated house and warm up enough to digest.
Since I gave him a warm soak and put the CHE in his outdoor digs - he's been out and about the yard - happily munching in his food garden and weeds in my lawn! I should be able to take the CHE out in the next few weeks as it will start to get warmer during the nights where he won't need extra heat!