I have been using the Phoenix XL in 2.6, 2.8 R and out of 6 only 3 work. When they work they are fabulous, but my problem is the wicks are burnt to a crisp after a couple puffs and only at 3.7 v. So I have been having problems. But I do have two going well right now, even refilled the one no problem. But aaack, 50% duds is not good! I will try the lower R ones and see if they are any better. bnrk