I'd bet all the gold in my bank that the charges are tied to your account, similar to barrows degradation. Actually for this item, it's tied to the item. Or maybe it's to your account, but then you still can't trade it if you have any charges. I tried trading a DFS I had with 13 charges and it wouldn't let me. Same thing happens at any other number of charges (I just like 13). What do you mean by Barrows degradation? Like trading armor pieces that are half used?