I started this thread and used the Zippo heater this past hunting season. I filled it up once I got to my stand and they worked fine for 7-8 hrs. I had it in a hand muff (or whatever they are called) and held onto the warmer most of the time because I was afraid if it was on it's side that it would go out. I found that to be the case when I first filled it and ran the heater in the camper. I like it better than the disposable packets as they do not seem to get hot enough. I only have 1 right now but I will have 2 by next hunting season.